Techniques for reducing latency in a wireless home theater environment

ABSTRACT

A first playback device can include a wireless network interface, an audio input interface, one or more processors, and data storage. The data storage stores instructions that, when executed by the processors, cause the first playback device to determine a first radio frequency (RF) energy level associated with RF signal communications from a second playback device to the first playback device. The first playback device modifies a threshold RF energy level for holding off transmissions by the first playback device based on the first RF energy level. The first playback device receives multi-channel audio content via the audio input interface and detects an ambient RF energy level. Based on the ambient RF energy level and the threshold RF energy level, data that represents a channel of the multi-channel audio content is communicated by the first playback device to the second playback device for playback by the second playback device in synchrony with playback of one or more other channels of the multi-channel audio content by the first playback device.

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/984,656, filed on Mar. 3, 2020, titled “TECHNIQUES FOR REDUCINGLATENCY IN A WIRELESS HOME THEATER ENVIRONMENT,” which is incorporatedherein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure is related to consumer goods and, moreparticularly, to methods, systems, products, features, services, andother elements directed to media playback or some aspect thereof.

BACKGROUND

Options for accessing and listening to digital audio in an out-loudsetting were limited until 2002 when SONOS, Inc. began the developmentof a new type of playback system. Sonos then filed one of its firstpatent applications in 2003, entitled “Method for Synchronizing AudioPlayback between Multiple Networked Devices,” and began offering itsfirst media playback systems for sale in 2005. The Sonos Wireless HomeSound System enables people to experience music from many sources viaone or more networked playback devices. Through a software controlapplication installed on a controller (e.g., smartphone, tablet,computer, voice input device), one can play what she wants in any roomhaving a networked playback device. Media content (e.g., songs,podcasts, video sound) can be streamed to playback devices such thateach room with a playback device can play back corresponding differentmedia content. In addition, rooms can be grouped together forsynchronous playback of the same media content, and/or the same mediacontent can be heard in all rooms synchronously.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of the presently disclosed technologymay be better understood with regard to the following description,appended claims, and accompanying drawings, as listed below. A personskilled in the relevant art will understand that the features shown inthe drawings are for purposes of illustrations, and variations,including different and/or additional features and arrangements thereof,are possible.

FIG. 1A is a partial cutaway view of an environment having a mediaplayback system, in accordance with an example.

FIG. 1B is a schematic diagram of the media playback system of FIG. 1Aand one or more networks, in accordance with an example.

FIG. 1C is a block diagram of a playback device, in accordance with anexample.

FIG. 1D is a block diagram of a playback device, in accordance with anexample.

FIG. 1E is a block diagram of a network microphone device, in accordancewith an example.

FIG. 1F is a block diagram of a network microphone device, in accordancewith an example.

FIG. 1G is a block diagram of a playback device, in accordance with anexample.

FIG. 1H is a partially schematic diagram of a control device, inaccordance with an example.

FIGS. 1I through 1L are schematic diagrams of corresponding mediaplayback system zones, in accordance with an example.

FIG. 1M is a schematic diagram of media playback system areas, inaccordance with an example.

FIG. 2 illustrates an example of a home theater environment, inaccordance with an example.

FIGS. 3A and 3B each illustrate an example methodology that can beutilized by a master playback device (MPD) of the home theaterenvironment to communicate audio content to a satellite playback device(SPD) of the home theater environment, in accordance with an example.

FIG. 4 illustrates a logical diagram of circuitry of the MPD that canmitigate issues that can occur due to wireless interference, inaccordance with an example.

FIG. 5 illustrates operations that can be performed by a processorand/or a wireless interface of the circuitry to mitigate theinterference issues, in accordance with an example.

FIGS. 6A and 6B are timing diagrams that illustrate modification of theRSSI threshold, in accordance with an example.

FIG. 7 illustrates a logical diagram of a wireless interface that canperform the RSSI modification functionality, in accordance with anexample.

FIG. 8 illustrates a variation of the operations performed in FIG. 5, inaccordance with an example.

The drawings are for the purpose of illustrating example embodiments,but those of ordinary skill in the art will understand that thetechnology disclosed herein is not limited to the arrangements and/orinstrumentality shown in the drawings.

DETAILED DESCRIPTION I. Overview

Home theater systems have stringent latency requirements in order tomaintain lip-synchrony between the audio being played back by the hometheater system and the video content being displayed by a television.These stringent latency requirements arise from the fact thattelevisions typically are designed to minimize the delay between receiptof media content (e.g., video content and corresponding audio content)from an external source (e.g., a media player, a gaming console, etc.)and output of that media content. As a result, the television willoutput the audio content and start processing the video content fordisplay immediately upon receipt of the media content. Thus, the hometheater system may need to process the audio content received from thetelevision in parallel with the television processing the video content.Given this architecture, the home theater system cannot takesubstantially longer to output the audio content than the televisiontakes to process the video content without the audio being delayedrelative to the video (e.g., losing lip-synchrony). As a result, thehome theater system needs to render the audio content within tens ofmilliseconds of receipt from the television in order to achievelip-synchronization.

For home theater systems that employ a wireless network to transfer theaudio to the requisite playback devices in the home theater system, thetime spent packetizing and transmitting the audio content over thewireless network can be quite substantial (e.g., multiple milliseconds).Further, the time required to packetize and transmit the audio over thewireless network increases with the number of wireless speakers in thehome theater system. For example, a home theater system that includestwo playback devices communicating over the wireless network may needsubstantially less time to packetize and transmit all of the audio thana similar home theater system including four or more playback devices.As a result, conventional home theater systems that communicate theaudio data over a wireless network typically meet the stringent latencyrequirements for lip-synchronization by severely limiting the number ofplayback devices in the home theater system to no more than fourplayback devices (e.g., a front soundbar, a subwoofer, a left rearspeaker, and a right rear speaker).

Aspects of the present disclosure manifest an appreciation that onesource of latency in wireless communication is the collision avoidancemechanism integrated into many wireless communication standards. Thesecollision avoidance mechanisms typically stop transmission of data froma transmit buffer when activity is detected in a communication channel.The goal of these collision avoidance mechanisms is to avoid a scenariowhere a device attempts to transmit data in a communication channelwhile the same device (or another nearby device) is simultaneouslyattempting to receive data in the same communication channel. Forexample, a device may prepare a packet for transmission on a particularchannel in wireless local area network (WLAN). In this example, thedevice may detect activity on the channel and wait for the activity toclear before transmitting the packet. In the wireless context, thesecollision avoidance mechanisms can be triggered by a variety ofirrelevant radio frequency (RF) energy in a channel such as operation ofan appliance that generates RF energy (e.g., a microwave) and/ortransmissions from unrelated network equipment (e.g., a neighbors accesspoint (AP)). In noisy environments (e.g., densely populated areas suchas apartment complexes in an urban setting), the delay introduced by thecollision detection mechanism can be substantial and interfere withoperation of a device in latency sensitive situatations, such asplayback of audio content in a home theater system. For example, thewireless transmissions of audio content may be delayed to the pointwhere the audio content fails to reach a playback device before thedesignated playback time of that audio content. In such an instance, theplayback device may either playback the audio late (e.g., out-of-syncwith the video and/or causing an echo if other speakers get the audioin-time) or simply not playback any audio (e.g., have the playbackdevice dropout).

Embodiments described herein relate to techniques to advantageouslyreduce the latency in wireless transmission of audio data betweenplayback devices. In these embodiments, the latency may be reduced bymitigating the delays that otherwise would be introduced by a collisionavoidance mechanism. For example, the playback device may monitor thereceived signal strength of packets from a set of one or more devices ofinterest that the playback device wants to communicate with. After theplayback device has identified the set of one or more devices ofinterest, the playback device may reduce the sensitivity of thecollision avoidance mechanism based on the received signal strength ofthe transmissions from the set of one or more devices of interest. Inparticular, the collision avoidance mechanism may be strategicallydesensitized such that the collision avoidance mechanism is stilltriggered by transmissions from any of the devices of interest whilebeing less likely to be triggered by other sources (e.g., operation ofmicrowaves, communication by devices other than the devices of interest,etc.). By strategically desensitizing the collision avoidance mechanism,the playback device maintains reliable communication with the devices ofinterest while ignoring other sources of RF energy so as to reduce thenumber of instances where the collision avoidance mechanism impedespacket transmissions.

In the context of a home theater system, the one or more devices ofinterest may include the other playback devices within the home theatersystem. For example, a soundbar in a surround sound system comprisingthe soundbar, a subwoofer, and two rear satellites may identify thesubwoofer and the two rear satellites as devices of interest. In thisexample, the soundbar may strategically reduce the sensitivity of thecollision avoidance mechanism such that the collision avoidancemechanism is not triggered by activity in a channel with a signalstrength that is below (e.g., by a margin) the signal strength ofcommunications from the subwoofer and the two rear satellites. Thus, thesoundbar can effectively ignore activity in the channel that is unlikelyto be a transmission from the subwoofer and the two rear satelliteswithout compromising communication with the subwoofer and the two rearsatellites. As a result, the amount of latency introduced by thecollision avoidance mechanism is substantially reduced (particularly innoisy environments). This reduction in latency may advatangeously enablethe home theater system to support wireless communication of audio databetween a larger number of playback devices than conventional techniqueswhile still meeting the stringent latency requirements forlip-synchronization with the video output by a television. The abilityto support wireless communication of audio data between a larger numberof playback devices may advantageously enable support for moresophisticated audio standards, such as DOLBY ATMOS.

Any of a variety of approaches may be employed to effectuate a dynamicsensitivity adjustment of the collision avoidance mechanism inaccordance with the latency reduction techniques described herein. Insome implementations, the sensitivity adjustment of the collisionavoidance mechanism may be achieved by modifying (e.g., via programinstructions executed by one or more processors) one or more parametersassociated with the collision avoidance mechanism. For example, thecollision avoidance mechanism may employ one or more thresholds thatgovern when the collision avoidance mechanism activates (e.g., a signaldetect threshold and/or an energy detect threshold in 802.11 standards).In this example, the senility of the collision detection mechanism maybe adjusted by modifying the one or more thresholds (e.g., via programinstructions executed by the one or more processors). Additionally (oralternatively), the sensitivity adjustment of the collision avoidancemechanism may be achieved by dynamically modifying an amount of gain(e.g., amplification) applied to a wireless signal detected by anantenna. For example, the RF energy levels for a detected wirelesssignal that are employed by the collision detection mechanism aretypically measured after the gain from electrical components (e.g.,amplifiers) has already been applied. Thus, the gain provided by thoseelectrical components may be modified while the RF energy level for awireless signal is being measured for the collision avoidance mechanismto change the value of the RF energy level seen by the collisionavoidance mechanism. As a result, the RF energy level seen by thecollision avoidance mechanism may be, for example, decreased to reducethe probability that the collision detection mechanism impedes a packettransmission. The gain applied to a detected wireless signal may bemodified in any of a variety of ways. For example, the gain may bereduced by bypassing one or more amplifiers (e.g., by closing a bypassswitch coupled in parallel with an amplifier) coupled to the antenna.Similarly, the gain may be increased by activating one or moreamplifiers (e.g., by opening a bypass switch coupled in parallel with anamplifier) coupled to the antenna.

The latency reduction techniques described herein may be readily appliedto any of a variety of devices including, for example, a playback devicecapable of operating in a home theater system. The playback device mayinclude a wireless network interface (e.g., comprising a wirelesstransceiver such as an 802.11 wireless transceiver), an audio inputinterface (e.g., comprising a port and/or associated circuitryconfigured to receive audio content from an external source, such as atelevision, a DVD player, a gaming console, a video streaming device,etc.), one or more processors, and data storage. The data storage storesinstructions that when executed by the one or more processors, cause theplayback device to determine a first RF energy level associated with RFsignal communications from a another playback device to the playbackdevice. The playback device may modify a threshold RF energy level forholding off transmissions (e.g., an threshold associated with acollision detection mechanism such as a signal detect threshold and/oran energy detect threshold in 802.11) by the playback device based onthe first RF energy level. The playback device may receive multi-channelaudio content via the audio input interface and detect an ambient RFenergy level. Based on the ambient RF energy level and the threshold RFenergy level, data that represents a channel of the multi-channel audiocontent may be communicated by the playback device to the other playbackdevice for playback by the other playback device in synchrony withplayback of one or more other channels of the multi-channel audiocontent by the playback device.

While some examples described herein may refer to functions performed bygiven actors such as “users,” “listeners,” and/or other entities, itshould be understood that this is for purposes of explanation only. Theclaims should not be interpreted to require action by any such exampleactor unless explicitly required by the language of the claimsthemselves.

In the Figures, identical reference numbers identify generally similar,and/or identical, elements. To facilitate the discussion of anyparticular element, the most significant digit or digits of a referencenumber refers to the Figure in which that element is first introduced.For example, element 110 a is first introduced and discussed withreference to FIG. 1A. Many of the details, dimensions, angles and otherfeatures shown in the Figures are merely illustrative of particularembodiments of the disclosed technology. Accordingly, other embodimentscan have other details, dimensions, angles, and features withoutdeparting from the spirit or scope of the disclosure. In addition, thoseof ordinary skill in the art will appreciate that further embodiments ofthe various disclosed technologies can be practiced without several ofthe details described below.

II. Suitable Operating Environment

FIG. 1A is a partial cutaway view of a media playback system 100distributed in an environment 101 (e.g., a house). The media playbacksystem 100 comprises one or more playback devices 110 (identifiedindividually as playback devices 110 a-n), one or more networkmicrophone devices (“NMDs”), 120 (identified individually as NMDs 120a-c), and one or more control devices 130 (identified individually ascontrol devices 130 a and 130 b).

As used herein the term “playback device” can generally refer to anetwork device configured to receive, process, and output data of amedia playback system. For example, a playback device can be a networkdevice that receives and processes audio content. In some embodiments, aplayback device includes one or more transducers or speakers powered byone or more amplifiers. In other embodiments, however, a playback deviceincludes one of (or neither of) the speaker and the amplifier. Forinstance, a playback device can comprise one or more amplifiersconfigured to drive one or more speakers external to the playback devicevia a corresponding wire or cable.

Moreover, as used herein the term NMD (i.e., a “network microphonedevice”) can generally refer to a network device that is configured foraudio detection. In some embodiments, an NMD is a stand-alone deviceconfigured primarily for audio detection. In other embodiments, an NMDis incorporated into a playback device (or vice versa).

The term “control device” can generally refer to a network deviceconfigured to perform functions relevant to facilitating user access,control, and/or configuration of the media playback system 100.

Each of the playback devices 110 is configured to receive audio signalsor data from one or more media sources (e.g., one or more remoteservers, one or more local devices) and play back the received audiosignals or data as sound. The one or more NMDs 120 are configured toreceive spoken word commands, and the one or more control devices 130are configured to receive user input. In response to the received spokenword commands and/or user input, the media playback system 100 can playback audio via one or more of the playback devices 110. In certainembodiments, the playback devices 110 are configured to commenceplayback of media content in response to a trigger. For instance, one ormore of the playback devices 110 can be configured to play back amorning playlist upon detection of an associated trigger condition(e.g., presence of a user in a kitchen, detection of a coffee machineoperation). In some embodiments, for example, the media playback system100 is configured to play back audio from a first playback device (e.g.,the playback device 100 a) in synchrony with a second playback device(e.g., the playback device 100 b). Interactions between the playbackdevices 110, NMDs 120, and/or control devices 130 of the media playbacksystem 100 configured in accordance with the various embodiments of thedisclosure are described in greater detail below with respect to FIGS.1B-1M.

In the illustrated embodiment of FIG. 1A, the environment 101 comprisesa household having several rooms, spaces, and/or playback zones,including (clockwise from upper left) a master bathroom 101 a, a masterbedroom 101 b, a second bedroom 101 c, a family room or den 101 d, anoffice 101 e, a living room 101 f, a dining room 101 g, a kitchen 101 h,and an outdoor patio 101 i. While certain embodiments and examples aredescribed below in the context of a home environment, the technologiesdescribed herein may be implemented in other types of environments. Insome embodiments, for example, the media playback system 100 can beimplemented in one or more commercial settings (e.g., a restaurant,mall, airport, hotel, a retail or other store), one or more vehicles(e.g., a sports utility vehicle, bus, car, a ship, a boat, an airplane),multiple environments (e.g., a combination of home and vehicleenvironments), and/or another suitable environment where multi-zoneaudio may be desirable.

The media playback system 100 can comprise one or more playback zones,some of which may correspond to the rooms in the environment 101. Themedia playback system 100 can be established with one or more playbackzones, after which additional zones may be added, or removed to form,for example, the configuration shown in FIG. 1A. Each zone may be givena name according to a different room or space such as the office 101 e,master bathroom 101 a, master bedroom 101 b, the second bedroom 101 c,kitchen 101 h, dining room 101 g, living room 101 f, and/or the balcony101 i. In some aspects, a single playback zone may include multiplerooms or spaces. In certain aspects, a single room or space may includemultiple playback zones.

In the illustrated embodiment of FIG. 1A, the master bathroom 101 a, thesecond bedroom 101 c, the office 101 e, the living room 101 f, thedining room 101 g, the kitchen 101 h, and the outdoor patio 101 i eachinclude one playback device 110, and the master bedroom 101 b and theden 101 d include a plurality of playback devices 110. In the masterbedroom 101 b, the playback devices 110 l and 110 m may be configured,for example, to play back audio content in synchrony as individual onesof playback devices 110, as a bonded playback zone, as a consolidatedplayback device, and/or any combination thereof. Similarly, in the den101 d, the playback devices 110 h-j can be configured, for instance, toplay back audio content in synchrony as individual ones of playbackdevices 110, as one or more bonded playback devices, and/or as one ormore consolidated playback devices. Additional details regarding bondedand consolidated playback devices are described below with respect toFIGS. 1B and 1M.

In some aspects, one or more of the playback zones in the environment101 may each be playing different audio content. For instance, a usermay be grilling on the patio 101 i and listening to hip hop music beingplayed by the playback device 110 c while another user is preparing foodin the kitchen 101 h and listening to classical music played by theplayback device 110 b. In another example, a playback zone may play thesame audio content in synchrony with another playback zone. Forinstance, the user may be in the office 101 e listening to the playbackdevice 110 f playing back the same hip hop music being played back byplayback device 110 c on the patio 101 i. In some aspects, the playbackdevices 110 c and 110 f play back the hip hop music in synchrony suchthat the user perceives that the audio content is being playedseamlessly (or at least substantially seamlessly) while moving betweendifferent playback zones. Additional details regarding audio playbacksynchronization among playback devices and/or zones can be found, forexample, in U.S. Pat. No. 8,234,395 entitled, “System and method forsynchronizing operations among a plurality of independently clockeddigital data processing devices,” which is incorporated herein byreference in its entirety.

a. Suitable Media Playback System

FIG. 1B is a schematic diagram of the media playback system 100 and acloud network 102. For ease of illustration, certain devices of themedia playback system 100 and the cloud network 102 are omitted fromFIG. 1B. One or more communication links 103 (referred to hereinafter as“the links 103”) communicatively couple the media playback system 100and the cloud network 102.

The links 103 can comprise, for example, one or more wired networks, oneor more wireless networks, one or more wide area networks (WAN), one ormore local area networks (LAN), one or more personal area networks(PAN), one or more telecommunication networks (e.g., one or more GlobalSystem for Mobiles (GSM) networks, Code Division Multiple Access (CDMA)networks, Long-Term Evolution (LTE) networks, 5G communication networknetworks, and/or other suitable data transmission protocol networks),etc. The cloud network 102 is configured to deliver media content (e.g.,audio content, video content, photographs, social media content) to themedia playback system 100 in response to a request transmitted from themedia playback system 100 via the links 103. In some embodiments, thecloud network 102 is further configured to receive data (e.g., voiceinput data) from the media playback system 100 and correspondinglytransmit commands and/or media content to the media playback system 100.

The cloud network 102 comprises computing devices 106 (identifiedseparately as a first computing device 106 a, a second computing device106 b, and a third computing device 106 c). The computing devices 106can comprise individual computers or servers, such as, for example, amedia streaming service server storing audio and/or other media content,a voice service server, a social media server, a media playback systemcontrol server, etc. In some embodiments, one or more of the computingdevices 106 comprise modules of a single computer or server. In certainembodiments, one or more of the computing devices 106 comprise one ormore modules, computers, and/or servers. Moreover, while the cloudnetwork 102 is described above in the context of a single cloud network,in some embodiments, the cloud network 102 comprises a plurality ofcloud networks comprising communicatively coupled computing devices.Furthermore, while the cloud network 102 is shown in FIG. 1B as havingthree of the computing devices 106, in some embodiments, the cloudnetwork 102 comprises fewer (or more than) three computing devices 106.

The media playback system 100 is configured to receive media contentfrom the networks 102 via the links 103. The received media content cancomprise, for example, a Uniform Resource Identifier (URI) and/or aUniform Resource Locator (URL). For instance, in some examples, themedia playback system 100 can stream, download, or otherwise obtain datafrom a URI or a URL corresponding to the received media content. Anetwork 104 communicatively couples the links 103 and at least a portionof the devices (e.g., one or more of the playback devices 110, NMDs 120,and/or control devices 130) of the media playback system 100. Thenetwork 104 can include, for example, a wireless network (e.g., a WiFinetwork, a Bluetooth, a Z-Wave network, a ZigBee, and/or other suitablewireless communication protocol network) and/or a wired network (e.g., anetwork comprising Ethernet, Universal Serial Bus (USB), and/or anothersuitable wired communication). As those of ordinary skill in the artwill appreciate, as used herein, “WiFi” can refer to several differentcommunication protocols including, for example, Institute of Electricaland Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.11ad, 802.11af, 802.11ah, 802.11ai, 802.11aj, 802.11aq,802.11ax, 802.11ay, 802.15, etc. transmitted at 2.4 Gigahertz (GHz), 5GHz, 6 GHz, and/or another suitable frequency.

In some embodiments, the network 104 comprises a dedicated communicationnetwork that the media playback system 100 uses to transmit messagesbetween individual devices and/or to transmit media content to and frommedia content sources (e.g., one or more of the computing devices 106).In certain embodiments, the network 104 is configured to be accessibleonly to devices in the media playback system 100, thereby reducinginterference and competition with other household devices. In otherembodiments, however, the network 104 comprises an existing householdcommunication network (e.g., a household WiFi network). In someembodiments, the links 103 and the network 104 comprise one or more ofthe same networks. In some aspects, for example, the links 103 and thenetwork 104 comprise a telecommunication network (e.g., an LTE network,a 5G network). Moreover, in some embodiments, the media playback system100 is implemented without the network 104, and devices comprising themedia playback system 100 can communicate with each other, for example,via one or more direct connections, PANs, telecommunication networks,and/or other suitable communication links.

In some embodiments, audio content sources may be regularly added orremoved from the media playback system 100. In some embodiments, forexample, the media playback system 100 performs an indexing of mediaitems when one or more media content sources are updated, added to,and/or removed from the media playback system 100. The media playbacksystem 100 can scan identifiable media items in some or all foldersand/or directories accessible to the playback devices 110, and generateor update a media content database comprising metadata (e.g., title,artist, album, track length) and other associated information (e.g.,URIs, URLs) for each identifiable media item found. In some embodiments,for example, the media content database is stored on one or more of theplayback devices 110, network microphone devices 120, and/or controldevices 130.

In the illustrated embodiment of FIG. 1B, the playback devices 110 l and110 m comprise a group 107 a. The playback devices 110 l and 110 m canbe positioned in different rooms in a household and be grouped togetherin the group 107 a on a temporary or permanent basis based on user inputreceived at the control device 130 a and/or another control device 130in the media playback system 100. When arranged in the group 107 a, theplayback devices 110 l and 110 m can be configured to play back the sameor similar audio content in synchrony from one or more audio contentsources. In certain embodiments, for example, the group 107 a comprisesa bonded zone in which the playback devices 110 l and 110 m compriseleft audio and right audio channels, respectively, of multi-channelaudio content, thereby producing or enhancing a stereo effect of theaudio content. In some embodiments, the group 107 a includes additionalplayback devices 110. In other embodiments, however, the media playbacksystem 100 omits the group 107 a and/or other grouped arrangements ofthe playback devices 110. Additional details regarding groups and otherarrangements of playback devices are described in further detail belowwith respect to FIGS. 1-I through IM.

The media playback system 100 includes the NMDs 120 a and 120 d, eachcomprising one or more microphones configured to receive voiceutterances from a user. In the illustrated embodiment of FIG. 1B, theNMD 120 a is a standalone device and the NMD 120 d is integrated intothe playback device 110 n. The NMD 120 a, for example, is configured toreceive voice input 121 from a user 123. In some embodiments, the NMD120 a transmits data associated with the received voice input 121 to avoice assistant service (VAS) configured to (i) process the receivedvoice input data and (ii) transmit a corresponding command to the mediaplayback system 100. In some aspects, for example, the computing device106 c comprises one or more modules and/or servers of a VAS (e.g., a VASoperated by one or more of SONOS®, AMAZON®, GOOGLE® APPLE®, MICROSOFT®).The computing device 106 c can receive the voice input data from the NMD120 a via the network 104 and the links 103. In response to receivingthe voice input data, the computing device 106 c processes the voiceinput data (i.e., “Play Hey Jude by The Beatles”), and determines thatthe processed voice input includes a command to play a song (e.g., “HeyJude”). The computing device 106 c accordingly transmits commands to themedia playback system 100 to play back “Hey Jude” by the Beatles from asuitable media service (e.g., via one or more of the computing devices106) on one or more of the playback devices 110.

b. Suitable Playback Devices

FIG. 1C is a block diagram of the playback device 110 a comprising aninput/output 111. The input/output 111 can include an analog I/O 111 a(e.g., one or more wires, cables, and/or other suitable communicationlinks configured to carry analog signals) and/or a digital I/O 111 b(e.g., one or more wires, cables, or other suitable communication linksconfigured to carry digital signals). In some embodiments, the analogI/O 111 a is an audio line-in input connection comprising, for example,an auto-detecting 3.5 mm audio line-in connection. In some embodiments,the digital I/O 111 b comprises a Sony/Philips Digital Interface Format(S/PDIF) communication interface and/or cable and/or a Toshiba Link(TOSLINK) cable. In some embodiments, the digital I/O 111 b comprises aHigh-Definition Multimedia Interface (HDMI) interface and/or cable. Insome embodiments, the digital I/O 111 b includes one or more wirelesscommunication links comprising, for example, a radio frequency (RF),infrared, WiFi, Bluetooth, or another suitable communication protocol.In certain embodiments, the analog I/O 111 a and the digital 111 bcomprise interfaces (e.g., ports, plugs, jacks) configured to receiveconnectors of cables transmitting analog and digital signals,respectively, without necessarily including cables.

The playback device 110 a, for example, can receive media content (e.g.,audio content comprising music and/or other sounds) from a local audiosource 105 via the input/output 111 (e.g., a cable, a wire, a PAN, aBluetooth connection, an ad hoc wired or wireless communication network,and/or another suitable communication link). The local audio source 105can comprise, for example, a mobile device (e.g., a smartphone, atablet, a laptop computer) or another suitable audio component (e.g., atelevision, a desktop computer, an amplifier, a phonograph, a Blu-rayplayer, a memory storing digital media files). In some aspects, thelocal audio source 105 includes local music libraries on a smartphone, acomputer, networked-attached storage (NAS), and/or another suitabledevice configured to store media files. In certain embodiments, one ormore of the playback devices 110, NMDs 120, and/or control devices 130comprise the local audio source 105. In other embodiments, however, themedia playback system omits the local audio source 105 altogether. Insome embodiments, the playback device 110 a does not include aninput/output 111 and receives all audio content via the network 104.

The playback device 110 a further comprises electronics 112, a userinterface 113 (e.g., one or more buttons, knobs, dials, touch-sensitivesurfaces, displays, touchscreens), and one or more transducers 114(referred to hereinafter as “the transducers 114”). The electronics 112is configured to receive audio from an audio source (e.g., the localaudio source 105) via the input/output 111, one or more of the computingdevices 106 a-c via the network 104 (FIG. 1B)), amplify the receivedaudio, and output the amplified audio for playback via one or more ofthe transducers 114. In some embodiments, the playback device 110 aoptionally includes one or more microphones 115 (e.g., a singlemicrophone, a plurality of microphones, a microphone array) (hereinafterreferred to as “the microphones 115”). In certain embodiments, forexample, the playback device 110 a having one or more of the optionalmicrophones 115 can operate as an NMD configured to receive voice inputfrom a user and correspondingly perform one or more operations based onthe received voice input.

In the illustrated embodiment of FIG. 1C, the electronics 112 compriseone or more processors 112 a (referred to hereinafter as “the processors112 a”), memory 112 b, software components 112 c, a network interface112 d, one or more audio processing components 112 g (referred tohereinafter as “the audio components 112 g”), one or more audioamplifiers 112 h (referred to hereinafter as “the amplifiers 112 h”),and power 112 i (e.g., one or more power supplies, power cables, powerreceptacles, batteries, induction coils, Power-over Ethernet (POE)interfaces, and/or other suitable sources of electric power). In someembodiments, the electronics 112 optionally include one or more othercomponents 112 j (e.g., one or more sensors, video displays,touchscreens, battery charging bases).

The processors 112 a can comprise clock-driven computing component(s)configured to process data, and the memory 112 b can comprise acomputer-readable medium (e.g., a tangible, non-transitorycomputer-readable medium, data storage loaded with one or more of thesoftware components 112 c) configured to store instructions forperforming various operations and/or functions. The processors 112 a areconfigured to execute the instructions stored on the memory 112 b toperform one or more of the operations. The operations can include, forexample, causing the playback device 110 a to retrieve audio data froman audio source (e.g., one or more of the computing devices 106 a-c(FIG. 1B)), and/or another one of the playback devices 110. In someembodiments, the operations further include causing the playback device110 a to send audio data to another one of the playback devices 110 aand/or another device (e.g., one of the NMDs 120). Certain embodimentsinclude operations causing the playback device 110 a to pair withanother of the one or more playback devices 110 to enable amulti-channel audio environment (e.g., a stereo pair, a bonded zone).

The processors 112 a can be further configured to perform operationscausing the playback device 110 a to synchronize playback of audiocontent with another of the one or more playback devices 110. As thoseof ordinary skill in the art will appreciate, during synchronousplayback of audio content on a plurality of playback devices, a listenerwill preferably be unable to perceive time-delay differences betweenplayback of the audio content by the playback device 110 a and the otherone or more other playback devices 110. Additional details regardingaudio playback synchronization among playback devices can be found, forexample, in U.S. Pat. No. 8,234,395, which was incorporated by referenceabove.

In some embodiments, the memory 112 b is further configured to storedata associated with the playback device 110 a, such as one or morezones and/or zone groups of which the playback device 110 a is a member,audio sources accessible to the playback device 110 a, and/or a playbackqueue that the playback device 110 a (and/or another of the one or moreplayback devices) can be associated with. The stored data can compriseone or more state variables that are periodically updated and used todescribe a state of the playback device 110 a. The memory 112 b can alsoinclude data associated with a state of one or more of the other devices(e.g., the playback devices 110, NMDs 120, control devices 130) of themedia playback system 100. In some aspects, for example, the state datais shared during predetermined intervals of time (e.g., every 5 seconds,every 10 seconds, every 60 seconds) among at least a portion of thedevices of the media playback system 100, so that one or more of thedevices have the most recent data associated with the media playbacksystem 100.

The network interface 112 d is configured to facilitate transmission ofdata between the playback device 110 a and one or more other devices ona data network such as, for example, the links 103 and/or the network104 (FIG. 1B). The network interface 112 d is configured to transmit andreceive data corresponding to media content (e.g., audio content, videocontent, text, photographs) and other signals (e.g., non-transitorysignals) comprising digital packet data including an Internet Protocol(IP)-based source address and/or an IP-based destination address. Thenetwork interface 112 d can parse the digital packet data such that theelectronics 112 properly receives and processes the data destined forthe playback device 110 a.

In the illustrated embodiment of FIG. 1C, the network interface 112 dcomprises one or more wireless interfaces 112 e (referred to hereinafteras “the wireless interface 112 e”). The wireless interface 112 e (e.g.,a suitable interface comprising one or more antennae) can be configuredto wirelessly communicate with one or more other devices (e.g., one ormore of the other playback devices 110, NMDs 120, and/or control devices130) that are communicatively coupled to the network 104 (FIG. 1B) inaccordance with a suitable wireless communication protocol (e.g., WiFi,Bluetooth, LTE). In some embodiments, the network interface 112 doptionally includes a wired interface 112 f (e.g., an interface orreceptacle configured to receive a network cable such as an Ethernet, aUSB-A, USB-C, and/or Thunderbolt cable) configured to communicate over awired connection with other devices in accordance with a suitable wiredcommunication protocol. In certain embodiments, the network interface112 d includes the wired interface 112 f and excludes the wirelessinterface 112 e. In some embodiments, the electronics 112 excludes thenetwork interface 112 d altogether and transmits and receives mediacontent and/or other data via another communication path (e.g., theinput/output 111).

The audio components 112 g are configured to process and/or filter datacomprising media content received by the electronics 112 (e.g., via theinput/output 111 and/or the network interface 112 d) to produce outputaudio signals. In some embodiments, the audio processing components 112g comprise, for example, one or more digital-to-analog converters (DAC),audio preprocessing components, audio enhancement components, digitalsignal processors (DSPs), and/or other suitable audio processingcomponents, modules, circuits, etc. In certain embodiments, one or moreof the audio processing components 112 g can comprise one or moresubcomponents of the processors 112 a. In some embodiments, theelectronics 112 omits the audio processing components 112 g. In someaspects, for example, the processors 112 a execute instructions storedon the memory 112 b to perform audio processing operations to producethe output audio signals.

The amplifiers 112 h are configured to receive and amplify the audiooutput signals produced by the audio processing components 112 g and/orthe processors 112 a. The amplifiers 112 h can comprise electronicdevices and/or components configured to amplify audio signals to levelssufficient for driving one or more of the transducers 114. In someembodiments, for example, the amplifiers 112 h include one or moreswitching or class-D power amplifiers. In other embodiments, however,the amplifiers include one or more other types of power amplifiers(e.g., linear gain power amplifiers, class-A amplifiers, class-Bamplifiers, class-AB amplifiers, class-C amplifiers, class-D amplifiers,class-E amplifiers, class-F amplifiers, class-G and/or class Hamplifiers, and/or another suitable type of power amplifier). In certainembodiments, the amplifiers 112 h comprise a suitable combination of twoor more of the foregoing types of power amplifiers.

Moreover, in some embodiments, individual ones of the amplifiers 112 hcorrespond to individual ones of the transducers 114. In otherembodiments, however, the electronics 112 includes a single one of theamplifiers 112 h configured to output amplified audio signals to aplurality of the transducers 114. In some other embodiments, theelectronics 112 omits the amplifiers 112 h.

The transducers 114 (e.g., one or more speakers and/or speaker drivers)receive the amplified audio signals from the amplifier 112 h and renderor output the amplified audio signals as sound (e.g., audible soundwaves having a frequency between about 20 Hertz (Hz) and 20 kilohertz(kHz)). In some embodiments, the transducers 114 can comprise a singletransducer. In other embodiments, however, the transducers 114 comprisea plurality of audio transducers. In some embodiments, the transducers114 comprise more than one type of transducer. For example, thetransducers 114 can include one or more low-frequency transducers (e.g.,subwoofers, woofers), mid-range frequency transducers (e.g., mid-rangetransducers, mid-woofers), and one or more high-frequency transducers(e.g., one or more tweeters). As used herein, “low frequency” cangenerally refer to audible frequencies below about 500 Hz, “mid-rangefrequency” can generally refer to audible frequencies between about 500Hz and about 2 kHz, and “high frequency” can generally refer to audiblefrequencies above 2 kHz. In certain embodiments, however, one or more ofthe transducers 114 comprise transducers that do not adhere to theforegoing frequency ranges. For example, one of the transducers 114 maycomprise a mid-woofer transducer configured to output sound atfrequencies between about 200 Hz and about 5 kHz.

By way of illustration, SONOS, Inc. presently offers (or has offered)for sale certain playback devices including, for example, a “SONOS ONE,”“PLAY:1,” “PLAY:3,” “PLAY:5,” “PLAYBAR,” “PLAYBASE,” “CONNECT:AMP,”“CONNECT,” and “SUB.” Other suitable playback devices may additionallyor alternatively be used to implement the playback devices of exampleembodiments disclosed herein. Additionally, one of ordinary skilled inthe art will appreciate that a playback device is not limited to theexamples described herein or to SONOS product offerings. In someembodiments, for example, one or more playback devices 110 compriseswired or wireless headphones (e.g., over-the-ear headphones, on-earheadphones, in-ear earphones). In other embodiments, one or more of theplayback devices 110 comprise a docking station and/or an interfaceconfigured to interact with a docking station for personal mobile mediaplayback devices. In certain embodiments, a playback device may beintegral to another device or component such as a television, a lightingfixture, or some other device for indoor or outdoor use. In someembodiments, a playback device omits a user interface and/or one or moretransducers. For example, FIG. 1D is a block diagram of a playbackdevice 110 p comprising the input/output 111 and electronics 112 withoutthe user interface 113 or transducers 114.

FIG. 1E is a block diagram of a bonded playback device 110 q comprisingthe playback device 110 a (FIG. 1C) sonically bonded with the playbackdevice 110 i (e.g., a subwoofer) (FIG. 1A). In the illustratedembodiment, the playback devices 110 a and 110 i are separate ones ofthe playback devices 110 housed in separate enclosures. In someembodiments, however, the bonded playback device 110 q comprises asingle enclosure housing both the playback devices 110 a and 110 i. Thebonded playback device 110 q can be configured to process and reproducesound differently than an unbonded playback device (e.g., the playbackdevice 110 a of FIG. 1C) and/or paired or bonded playback devices (e.g.,the playback devices 110 l and 110 m of FIG. 1B). In some embodiments,for example, the playback device 110 a is a full-range playback deviceconfigured to render low frequency, mid-range frequency, andhigh-frequency audio content, and the playback device 110 i is asubwoofer configured to render low-frequency audio content. In someaspects, the playback device 110 a, when bonded with the first playbackdevice, is configured to render only the mid-range and high-frequencycomponents of particular audio content, while the playback device 110 irenders the low-frequency component of the particular audio content. Insome embodiments, the bonded playback device 110 q includes additionalplayback devices and/or another bonded playback device.

c. Suitable Network Microphone Devices (NMDs)

FIG. 1F is a block diagram of the NMD 120 a (FIGS. 1A and 1B). The NMD120 a includes one or more voice processing components 124 (hereinafter“the voice components 124”) and several components described withrespect to the playback device 110 a (FIG. 1C) including the processors112 a, the memory 112 b, and the microphones 115. The NMD 120 aoptionally comprises other components also included in the playbackdevice 110 a (FIG. 1C), such as the user interface 113 and/or thetransducers 114. In some embodiments, the NMD 120 a is configured as amedia playback device (e.g., one or more of the playback devices 110),and further includes, for example, one or more of the audio components112 g (FIG. 1C), the amplifiers 114, and/or other playback devicecomponents. In certain embodiments, the NMD 120 a comprises an Internetof Things (IoT) device such as, for example, a thermostat, alarm panel,fire and/or smoke detector, etc. In some embodiments, the NMD 120 acomprises the microphones 115, the voice processing 124, and only aportion of the components of the electronics 112 described above withrespect to FIG. 1B. In some aspects, for example, the NMD 120 a includesthe processor 112 a and the memory 112 b (FIG. 1B), while omitting oneor more other components of the electronics 112. In some embodiments,the NMD 120 a includes additional components (e.g., one or more sensors,cameras, thermometers, barometers, hygrometers).

In some embodiments, an NMD can be integrated into a playback device.FIG. 1G is a block diagram of a playback device 110 r comprising an NMD120 d. The playback device 110 r can comprise many or all of thecomponents of the playback device 110 a and further include themicrophones 115 and voice processing 124 (FIG. 1F). The playback device110 r optionally includes an integrated control device 130 c. Thecontrol device 130 c can comprise, for example, a user interface (e.g.,the user interface 113 of FIG. 1B) configured to receive user input(e.g., touch input, voice input) without a separate control device. Inother embodiments, however, the playback device 110 r receives commandsfrom another control device (e.g., the control device 130 a of FIG. 1B).

Referring again to FIG. 1F, the microphones 115 are configured toacquire, capture, and/or receive sound from an environment (e.g., theenvironment 101 of FIG. 1A) and/or a room in which the NMD 120 a ispositioned. The received sound can include, for example, vocalutterances, audio played back by the NMD 120 a and/or another playbackdevice, background voices, ambient sounds, etc. The microphones 115convert the received sound into electrical signals to produce microphonedata. The voice processing 124 receives and analyzes the microphone datato determine whether a voice input is present in the microphone data.The voice input can comprise, for example, an activation word followedby an utterance including a user request. As those of ordinary skill inthe art will appreciate, an activation word is a word or other audio cuethat signifying a user voice input. For instance, in querying theAMAZON® VAS, a user might speak the activation word “Alexa.” Otherexamples include “Ok, Google” for invoking the GOOGLE® VAS and “Hey,Siri” for invoking the APPLE® VAS.

After detecting the activation word, voice processing 124 monitors themicrophone data for an accompanying user request in the voice input. Theuser request may include, for example, a command to control athird-party device, such as a thermostat (e.g., NEST® thermostat), anillumination device (e.g., a PHILIPS HUE® lighting device), or a mediaplayback device (e.g., a Sonos® playback device). For example, a usermight speak the activation word “Alexa” followed by the utterance “setthe thermostat to 68 degrees” to set a temperature in a home (e.g., theenvironment 101 of FIG. 1A). The user might speak the same activationword followed by the utterance “turn on the living room” to turn onillumination devices in a living room area of the home. The user maysimilarly speak an activation word followed by a request to play aparticular song, an album, or a playlist of music on a playback devicein the home.

d. Suitable Control Devices

FIG. 1H is a partially schematic diagram of the control device 130 a(FIGS. 1A and 1B). As used herein, the term “control device” can be usedinterchangeably with “controller” or “control system.” Among otherfeatures, the control device 130 a is configured to receive user inputrelated to the media playback system 100 and, in response, cause one ormore devices in the media playback system 100 to perform an action(s) oroperation(s) corresponding to the user input. In the illustratedembodiment, the control device 130 a comprises a smartphone (e.g., aniPhone™, an Android phone) on which media playback system controllerapplication software is installed. In some embodiments, the controldevice 130 a comprises, for example, a tablet (e.g., an iPad™), acomputer (e.g., a laptop computer, a desktop computer), and/or anothersuitable device (e.g., a television, an automobile audio head unit, anIoT device). In certain embodiments, the control device 130 a comprisesa dedicated controller for the media playback system 100. In otherembodiments, as described above with respect to FIG. 1G, the controldevice 130 a is integrated into another device in the media playbacksystem 100 (e.g., one more of the playback devices 110, NMDs 120, and/orother suitable devices configured to communicate over a network).

The control device 130 a includes electronics 132, a user interface 133,one or more speakers 134, and one or more microphones 135. Theelectronics 132 comprise one or more processors 132 a (referred tohereinafter as “the processors 132 a”), a memory 132 b, softwarecomponents 132 c, and a network interface 132 d. The processor 132 a canbe configured to perform functions relevant to facilitating user access,control, and configuration of the media playback system 100. The memory132 b can comprise data storage that can be loaded with one or more ofthe software components executable by the processor 302 to perform thosefunctions. The software components 132 c can comprise applicationsand/or other executable software configured to facilitate control of themedia playback system 100. The memory 112 b can be configured to store,for example, the software components 132 c, media playback systemcontroller application software, and/or other data associated with themedia playback system 100 and the user.

The network interface 132 d is configured to facilitate networkcommunications between the control device 130 a and one or more otherdevices in the media playback system 100, and/or one or more remotedevices. In some embodiments, the network interface 132 is configured tooperate according to one or more suitable communication industrystandards (e.g., infrared, radio, wired standards including IEEE 802.3,wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.15, 4G, LTE). The network interface 132 d can beconfigured, for example, to transmit data to and/or receive data fromthe playback devices 110, the NMDs 120, other ones of the controldevices 130, one of the computing devices 106 of FIG. 1B, devicescomprising one or more other media playback systems, etc. Thetransmitted and/or received data can include, for example, playbackdevice control commands, state variables, playback zone, and/or zonegroup configurations. For instance, based on user input received at theuser interface 133, the network interface 132 d can transmit a playbackdevice control command (e.g., volume control, audio playback control,audio content selection) from the control device 130 to one or more ofthe playback devices 100. The network interface 132 d can also transmitand/or receive configuration changes such as, for example,adding/removing one or more playback devices 100 to/from a zone,adding/removing one or more zones to/from a zone group, forming a bondedor consolidated player, separating one or more playback devices from abonded or consolidated player, among others. Additional description ofzones and groups can be found below with respect to FIGS. 1I through 1M.

The user interface 133 is configured to receive user input and canfacilitate control of the media playback system 100. The user interface133 includes media content art 133a (e.g., album art, lyrics, videos), aplayback status indicator 133 b (e.g., an elapsed and/or remaining timeindicator), media content information region 133 c, a playback controlregion 133 d, and a zone indicator 133 e. The media content informationregion 133 c can include a display of relevant information (e.g., title,artist, album, genre, release year) about media content currentlyplaying and/or media content in a queue or playlist. The playbackcontrol region 133 d can include selectable (e.g., via touch inputand/or via a cursor or another suitable selector) icons to cause one ormore playback devices in a selected playback zone or zone group toperform playback actions such as, for example, play or pause, fastforward, rewind, skip to next, skip to previous, enter/exit shufflemode, enter/exit repeat mode, enter/exit crossfade mode, etc. Theplayback control region 133 d may also include selectable icons tomodify equalization settings, playback volume, and/or other suitableplayback actions. In the illustrated embodiment, the user interface 133comprises a display presented on a touch screen interface of asmartphone (e.g., an iPhone™, an Android phone). In some embodiments,however, user interfaces of varying formats, styles, and interactivesequences may alternatively be implemented on one or more networkdevices to provide comparable control access to a media playback system.

The one or more speakers 134 (e.g., one or more transducers) can beconfigured to output sound to the user of the control device 130 a. Insome embodiments, the one or more speakers comprise individualtransducers configured to correspondingly output low frequencies,mid-range frequencies, and/or high frequencies. In some aspects, forexample, the control device 130 a is configured as a playback device(e.g., one of the playback devices 110). Similarly, in some embodiments,the control device 130 a is configured as an NMD (e.g., one of the NMDs120), receiving voice commands and other sounds via the one or moremicrophones 135.

The one or more microphones 135 can comprise, for example, one or morecondenser microphones, electret condenser microphones, dynamicmicrophones, and/or other suitable types of microphones or transducers.In some embodiments, two or more of the microphones 135 are arranged tocapture location information of an audio source (e.g., voice, audiblesound) and/or configured to facilitate filtering of background noise.Moreover, in certain embodiments, the control device 130 a is configuredto operate as a playback device and an NMD. In other embodiments,however, the control device 130 a omits the one or more speakers 134and/or the one or more microphones 135. For instance, the control device130 a may comprise a device (e.g., a thermostat, an IoT device, anetwork device) comprising a portion of the electronics 132 and the userinterface 133 (e.g., a touch screen) without any speakers ormicrophones.

e. Suitable Playback Device Configurations

FIGS. 1-I through 1M show example configurations of playback devices inzones and zone groups. Referring first to FIG. 1M, in one example, asingle playback device may belong to a zone. For example, the playbackdevice 110 g in the second bedroom 101 c (FIG. 1A) may belong to Zone C.In some implementations described below, multiple playback devices maybe “bonded” to form a “bonded pair” which together form a single zone.For example, the playback device 110 l (e.g., a left playback device)can be bonded to the playback device 110 l (e.g., a left playbackdevice) to form Zone A. Bonded playback devices may have differentplayback responsibilities (e.g., channel responsibilities). In anotherimplementation described below, multiple playback devices may be mergedto form a single zone. For example, the playback device 110 h (e.g., afront playback device) may be merged with the playback device 110 i(e.g., a subwoofer), and the playback devices 110 j and 110 k (e.g.,left and right surround speakers, respectively) to form a single Zone D.In another example, the playback devices 110 g and 110 h can be mergedto form a merged group or a zone group 108 b. The merged playbackdevices 110 g and 110 h may not be specifically assigned differentplayback responsibilities. That is, the merged playback devices 110 hand 110 i may, aside from playing audio content in synchrony, each playaudio content as they would if they were not merged.

Each zone in the media playback system 100 may be provided for controlas a single user interface (UI) entity. For example, Zone A may beprovided as a single entity named Master Bathroom. Zone B may beprovided as a single entity named Master Bedroom. Zone C may be providedas a single entity named Second Bedroom.

Playback devices that are bonded may have different playbackresponsibilities, such as responsibilities for certain audio channels.For example, as shown in FIG. 1-I, the playback devices 110 l and 110 mmay be bonded to produce or enhance a stereo effect of audio content. Inthis example, the playback device 110 l may be configured to play a leftchannel audio component, while the playback device 110 k may beconfigured to play a right channel audio component. In someimplementations, such stereo bonding may be referred to as “pairing.”

Additionally, bonded playback devices may have additional and/ordifferent respective speaker drivers. As shown in FIG. 1J, the playbackdevice 110 h named Front may be bonded with the playback device 110 inamed SUB. The Front device 110 h can be configured to render a range ofmid to high frequencies, and the SUB device 110 i can be configured torender low frequencies. When unbonded, however, the Front device 110 hcan be configured to render a full range of frequencies. As anotherexample, FIG. 1K shows the Front and SUB devices 110 h and 110 i furtherbonded with Left and Right playback devices 110 j and 110 k,respectively. In some implementations, the Right and Left devices 110 jand 102 k can be configured to form surround or “satellite” channels ofa home theater system. The bonded playback devices 110 h, 110 i, 110 j,and 110 k may form a single Zone D (FIG. 1M).

Playback devices that are merged may not have assigned playbackresponsibilities, and may each render the full range of audio contentthe respective playback device is capable of. Nevertheless, mergeddevices may be represented as a single UI entity (i.e., a zone, asdiscussed above). For instance, the playback devices 110 a and 110 n themaster bathroom have the single UI entity of Zone A. In one embodiment,the playback devices 110 a and 110 n may each output the full range ofaudio content each respective playback devices 110 a and 110 n arecapable of, in synchrony.

In some embodiments, an NMD is bonded or merged with another device soas to form a zone. For example, the NMD 120 b may be bonded with theplayback device 110 e, which together form Zone F, named Living Room. Inother embodiments, a stand-alone network microphone device may be in azone by itself. In other embodiments, however, a stand-alone networkmicrophone device may not be associated with a zone. Additional detailsregarding associating network microphone devices and playback devices asdesignated or default devices may be found, for example, in previouslyreferenced U.S. patent application Ser. No. 15/438,749.

Zones of individual, bonded, and/or merged devices may be grouped toform a zone group. For example, referring to FIG. 1M, Zone A may begrouped with Zone B to form a zone group 108 a that includes the twozones. Similarly, Zone G may be grouped with Zone H to form the zonegroup 108 b. As another example, Zone A may be grouped with one or moreother Zones C-I. The Zones A-I may be grouped and ungrouped in numerousways. For example, three, four, five, or more (e.g., all) of the ZonesA-I may be grouped. When grouped, the zones of individual and/or bondedplayback devices may play back audio in synchrony with one another, asdescribed in previously referenced U.S. Pat. No. 8,234,395. Playbackdevices may be dynamically grouped and ungrouped to form new ordifferent groups that synchronously play back audio content.

In various implementations, the zones in an environment may be thedefault name of a zone within the group or a combination of the names ofthe zones within a zone group. For example, Zone Group 108 b can have beassigned a name such as “Dining+Kitchen”, as shown in FIG. 1M. In someembodiments, a zone group may be given a unique name selected by a user.

Certain data may be stored in a memory of a playback device (e.g., thememory 112 c of FIG. 1C) as one or more state variables that areperiodically updated and used to describe the state of a playback zone,the playback device(s), and/or a zone group associated therewith. Thememory may also include the data associated with the state of the otherdevices of the media system, and shared from time to time among thedevices so that one or more of the devices have the most recent dataassociated with the system.

In some embodiments, the memory may store instances of various variabletypes associated with the states. Variables instances may be stored withidentifiers (e.g., tags) corresponding to a type. For example, certainidentifiers may be a first type “al” to identify playback device(s) of azone, a second type “b1” to identify playback device(s) that may bebonded in the zone, and a third type “c1” to identify a zone group towhich the zone may belong. As a related example, identifiers associatedwith the second bedroom 101 c may indicate that the playback device isthe only playback device of the Zone C and not in a zone group.Identifiers associated with the Den may indicate that the Den is notgrouped with other zones but includes bonded playback devices 110 h-110k. Identifiers associated with the Dining Room may indicate that theDining Room is part of the Dining+Kitchen zone group 108 b and thatdevices 110 b and 110 d are grouped (FIG. 1L). Identifiers associatedwith the Kitchen may indicate the same or similar information by virtueof the Kitchen being part of the Dining+Kitchen zone group 108 b. Otherexample zone variables and identifiers are described below.

In yet another example, the media playback system 100 may storevariables or identifiers representing other associations of zones andzone groups, such as identifiers associated with Areas, as shown in FIG.1M. An area may involve a cluster of zone groups and/or zones not withina zone group. For instance, FIG. 1M shows an Upper Area 109 a includingZones A-D, and a Lower Area 109 b including Zones E-I. In one aspect, anArea may be used to invoke a cluster of zone groups and/or zones thatshare one or more zones and/or zone groups of another cluster. Inanother aspect, this differs from a zone group, which does not share azone with another zone group.

Further examples of techniques for implementing Areas may be found, forexample, in U.S. application Ser. No. 15/682,506 filed Aug. 21, 2017 andtitled “Room Association Based on Name,” and U.S. Pat. No. 8,483,853filed Sep. 11, 2007, and titled “Controlling and manipulating groupingsin a multi-zone media system.” Each of these applications isincorporated herein by reference in its entirety. In some embodiments,the media playback system 100 may not implement Areas, in which case thesystem may not store variables associated with Areas.

III. Example Techniques for Reducing Latency in a Wireless Home TheaterEnvironment

As noted above, playback devices that are bonded may have differentplayback responsibilities, such as responsibilities for certain audiochannels. For example, as illustrated in FIG. 1K, in a home theaterenvironment, the Front and SUB devices 110 h and 110 i can be bondedwith Left and Right playback devices 110 j and 110 k, respectively.Further, in some implementations, the Right and Left devices 110 j and102 k can be configured to form surround or “satellite” channels of ahome theater system. The bonded playback devices 110 h, 110 i, 110 j,and 110 k may form a single Zone D (FIG. 1M).

FIG. 2 illustrates an example of a home theater environment 200. Shownin FIG. 2 are a television 205 and a Front playback device 210,hereinafter referred to as the master playback device (MPD). Otherplayback devices of the environment 200 include a Front Left playbackdevice 212 a, a Front Right playback device 212 b, a Subwoofer playbackdevice 212 c, a Rear Left playback device 212 d, and a Rear Rightplayback device 212 e. The other playback devices are hereinaftercollectively referred to as satellite playback devices (SPDs) 212. Otherdevices of the environment 200 can include a personal computer (PC) 220a and a wireless network router 220 b.

In the illustrated example, the MPD 210 receives audio content from thetelevision 205. For example, the MPD 210 can be positioned near thetelevision 205 and directed to a viewer who can be centrally positionedbetween the respective playback devices. The MPD 210 and the television205 can include analog and/or digital interfaces that facilitatecommunicating the multi-channel audio content such as a SPDIF RCAinterface, an HDMI interface (e.g., audio return channel (ARC) HDMIinterface), an optical interface (e.g., TOSLINK interface), etc. In someexamples, the MPD 210 and the television 205 can include wirelesscircuitry that facilitates communicating the audio content. For example,the audio content can be communicated via 802.11, BLUETOOTH, ZIGBEE,Z-WAVE, etc. The audio content can be associated with video contentdisplayed on the television 205.

The MPD 210 can wirelessly communicate/transmit different channels ofthe audio content (i.e., front-left channel, front-right channel,subwoofer channel, rear-left channel, and rear-right channel) to theSPDs 212. An example of the MPD 210 can communicate with the SPDs 212 ofthe environment 200 over one or more channels (e.g., one or more 20 Mhzchannels) of a 2.4 GHz spectrum, a 5 GHz spectrum, and/or a 6 GHzspectrum. Wireless communications performed within these spectrums canbe subject to certain regulations such as those specified by the FederalCommunications Commission (FCC) in the United States and/or otherregulatory bodies.

FIG. 3A illustrates an example of a methodology that can be utilized bythe MPD 210 to communicate audio content to the SPDs 212. Referring toFIG. 3A, the MPD 210 can utilize so-called “Round Robin” scheduling tocommunicate the audio content to the SPDs 212. For example, the MPD 210can receive a stream of audio content samples (300 a, 300 b, . . . 300N)from the television 205. The audio content samples 300 can becommunicated from the television 205 at any of a variety of ratesincluding, for example, 44.1 kilohertz (kHz), 48 kHz, 96 kHz, 176.2 kHz,and 192 kHz. The audio content samples 300 may comprise uncompressedaudio content (e.g., Pulse-Code Modulation (PCM) audio) and/orcompressed audio content (e.g., DOLBY audio such as DOLBY AC-3 audio,DOLBY E-AC-3 audio, DOLBY AC-4 audio, and DOLBY ATMOS audio). Thetelevision 205 outputs the audio content samples 300 while beginning theprocess of rendering the video content on a display (e.g., integratedinto the television 205). Given that the television 205 may take tens ofmilliseconds to successfully render the video content, the audio contentsamples 300 may be output before the corresponding video content isdisplayed (e.g., tens of milliseconds earlier). The MPD 210 maycoordinate playback of the audio content samples 300 in lip-synchronywith the video content being displayed on the television 205 such thatthere is no perceived audio delay (i.e., no lip-sinking issues areperceived) by the viewer. In this regard, it can be shown that in somecases, a delay of no more than 40 ms between the video content beingrendered and the audio content being heard is impercetable to theaverage viewer. The MPD 210 may achieve lip-synchony by, for example,exploiting one or more of the following periods of time: (1) a gapbetween the television 205 outputting the audio content samples 300 andtelevision 205 actually displaying the associated video content; and/or(2) an allowable delay between the video content being displayed and theassociated audio content being played back without losing lip-synchrony(e.g., up to 40 milliseconds).

After receiving a particular audio content sample 300 a, the MPD 210 canextract the channel samples 305 a (i.e., front-left, front-right, etc.)from the audio content sample 300 a and can communicate the channelsamples 305 a to the corresponding SPDs 212. In the illustrated examplesin FIG. 3A, the channel samples 305 a are communicated sequentially. Forexample, during a first interval, the MPD 210 can communicate thefront-left channel sample (FL1) associated with a first audio contentsample 300 a to the Front Left Playback device 212 a. During a secondinterval, the MPD 210 can communicate the front-right channel sample(FR1) associated with the first audio content sample 300 a to the FrontRight Playback device 212 b. During a third interval, the MPD 210 cancommunicate the subwoofer channel sample (SB1) associated with the firstaudio content sample 300 a to the subwoofer playback device 212 c.During a fourth interval, the MPD 210 can communicate the rear-leftchannel sample (RL1) associated with the first audio content sample 300a to the rear left playback device 212 d. During a fourth interval, theMPD 210 can communicate the rear-right channel sample (RR1) associatedwith the first audio content sample 300 a to the rear right playbackdevice 212 e. The same process can repeat with the arrival of subsequentaudio content samples from the television 205, such as audio contentsample 300 b through audio content sample 300N.

It should be appreciated that, in some examples, more than one of thechannel samples 305 a may be simultaneously communicated to the SPDs212. Simultaneous communication of audio content from the MPD 210 to theSPDs 212 may be accomplished in any of a variety of ways. For example,certain wireless communication standards (e.g., 802.11ax) includeorthogonal frequency-division multiple access (OFDMA) support thatenables a given wireless channel to be sub-divided into multiple smallersub-channels. Each of these sub-channels may be employed to communicatewith different devices independently from each other. In examples wherethe MPD 210 (and associated SPDs 212) support such a wirelesscommunication standard, the MPD 210 may simultaneously transmit audiosamples to a first SPD over a first sub-channel and transmit audiosamples to a second SPD over a second sub-channel within the samechannel as the first sub-channel. In other examples, the MPD 210 maycommunicate with the SPDs 212 using multiple RF channels. For example,the channel samples 305 a for a first subset of the SPDs 212 can becommunicated via a first RF channel and the channel camples 305 a for asecond subset of the SPDs can be communicated via a second RF channelthat is different from the first RF channel (e.g., a different channelin the same spectrum as the first RF channel or a different channel in adifferent spectrum than the first RF channel).

FIG. 3B illustrates an example of a methodology that can be utilized bythe MPD 210 to communicate audio content to the SPDs 212 that leveragesthe simultaneous communication capabilities described above. As shown,multiple channel samples may be transmitted simultaneously to differentplayback devices. For example, during a first interval, the MPD 210 cancommunicate both the front-left channel sample (FL1) associated with afirst audio content sample 300 a to the Front Left Playback device 212 aand the front-right channel sample (FR1) associated with the first audiocontent sample 300 a to the Front Right Playback device 212 b. During asecond interval, the MPD 210 can communicate the subwoofer channelsample (SB1) associated with the first audio content sample 300 a to thesubwoofer playback device 212 c. During a third interval, the MPD 210can communicate both the rear-left channel sample (RL1) associated withthe first audio content sample 300 a to the rear left playback device212 d and the rear-right channel sample (RR1) associated with the firstaudio content sample 300 a to the rear right playback device 212 e. Thesame process can repeat with the arrival of subsequent audio contentsamples from the television 205, such as audio content sample 300 bthrough audio content sample 300N.

It should be appreciated that the order in which the particular channelsamples 305 a are transmitted and the way in which the particularchannel samples 305 a are grouped for simultaneous transmission may varybased on the particular implementation. For example, the rear-leftchannel sample (RL1) and/or the rear-right channel sample (RR1) may betransmitted before the front-left channel sample (FL1) and/or thefront-right channel sample (FR1). Additionally (or alternatively), therear-left channel sample (RL1) may be transmitted simultaneously withthe front-left channel sample (FL1) and/or the the front-right channelsample (FR1). Thus, the particular channel samples 305 a may be orderedand/or grouped in any of a variety of ways.

It should be noted that the amount of time required to communicate thechannel samples 305 associated with a particular audio content sample300 can depend on the number of channels encoded in the audio contentsample 300 and/or the number of channels to be decoded from the audiocontent sample for playback by SPDs 212. For example, the total amountof time required to communicate the channel samples 305 may increase asthe total number of channels increases. This increase in the totalamount of time required to communicate the channel samples 305 canbecome problematic in home theater systems attempting to maintainlip-synchrony with video content being played back on the television205. For example, the total amount of time required to communicate therequisite channel samples 305 for audio content with a large number ofaudio channels (e.g., DOLBY ATMOS audio content) may be longer (e.g., incertain noisy environments) than the available time window to renderaudio output in lip-synchony.

As noted above, an example of the MPD 210 can communicate with the SPDs212 of the environment 200 via a 2.4 GHz spectrum, a 5 GHz spectrum,and/or a 6 GHz spectrum. And, as noted above, an example home theaterenvironment 200 can include other devices such as computers 220 a andwireless network routers 220 b that can, in some cases, communicatewithin the same spectrums. When this occurs, network traffic generatedby the other devices 220 can interfere with the communications betweenthe MPD 210 and the SPDs 212. Those home theater environments 200 thatare in densely populated areas (e.g., in apartment complexes and/or inurban environments) also may have interference from wireless devices ofnearby inhabitants (e.g., the wireless router of a neighbor, etc.). Theinterference can, in some cases, delay the communication of the channelsamples to the SPDs 212. And if the delay is severe enough, the MPD 210may be unable to successfully transmit the audio content samples 300 tothe SPDs 212 fast enough to maintain lip-synchrony. The interference canbe mitigated to an extent by monitoring the interference on multiplespectrums (e.g., two or more of: a 2.4 GHz spectrum, a 5 GHz spectrum,and a 6 GHz spectrum) and/or multiple channels (e.g., multiple channelson the 2.4 GHz spectrum, multiple channels on the 5 GHz spectrum,multiple channels on the 6 GHz spectrum, or a combination thereof) andcommunicating the channel samples via the spectrum and/or channels withthe highest connection quality (e.g., least interference, strongestsignal strength, etc.). However, the best channel and/or spectrum inparticularly noise environments may still not be of sufficient qualityto maintain lip-synchony.

FIG. 4 illustrates an example of a logical diagram of circuitry 400 ofthe MPD 210 that can further mitigate interference related issues. Forexample, the circuitry 400 can communicate audio content via the SPDs212 so that delay between the rendered video and the audio output fromthe SPDs is less than 40 ms. In some examples, the delay can be lessthan 20 ms. In yet other examples, the delay can be less than 5 ms.Referring to FIG. 4, the circuitry 400 includes a processor 405, awireless interface 410, and an antenna 415. The processor 405 cancorrespond to or include the capabilities of the processor 112 adescribed above. The wireless interface 410 can correspond to or includethe capabilities of the wireless interface 112 e described above.

An example of the wireless interface 410 can include a transmit buffer410 a, Collision Avoidance (CA) logic 410 b, transmitter (TX) circuitry410 c, receiver (RX) circuitry 410 d, and an RX/TX switch 410 e.

The transmit buffer 410 a can correspond to memory configured to storeTX data. For example, the transmit buffer 410 a can be sized to storeone or more audio content samples 300. The transmit buffer 410 a canreceive TX data from the processor 405, which can be in communicationand upstream of the transmit buffer 410 a. The transmit buffer 410 a cancommunicate the TX data to the TX circuitry 410 c, which can be incommunication and downstream of the transmit buffer 410 a. An example ofthe transmit buffer 410 a can correspond to a first-in-first-out (FIFO)memory. In this regard, the transmit buffer 410 a can output lower andupper watermark indications that can facilitate determining, by theprocessor 405, whether the number of samples stored in the transmitbuffer 410 a is below the lower watermark (e.g., a lower threshold) oris above the upper watermark (e.g., an upper threshold). That is, theprocessor 405 can determine whether the FIFO memory is almost empty oralmost full.

During operation, the processor 405 can be configured to communicate TXdata to the transmit buffer 410 a at a first rate when the data in thetransmit buffer 410 a falls below the lower watermark, and to stopsending TX data to the transmit buffer 410 a when the data in thetransmit buffer 410 a reaches the upper watermark. The transmit buffer410 a can be configured to communicate the TX data to the TX circuitry410 c at a second rate that can be lower than the first rate.

The CA logic 410 b can be configured to gate the communication of TXdata in the transmit buffer 410 a to the TX circuitry 410 c based on thesignal strength(s) (e.g., RSSI level, etc.) detected by the RX circuitry410 d within one or more channels of one or more frequency spectra. Inthis regard, the signal strength(s) may comprise one or more of thefollowing: (1) an RSSI level that can be a measure of the RF energylevel associated with a communication from a wireless device in achannel of a frequency spectrum; (2) a signal-to-noise ratio (SNR)associated with communication from a wireless device in a channel of afrequency spectrum (e.g., an SNR of a preamble transmission); and/or (3)an ambient RF energy level that can be a measure of the RF energy levelof energy within a channel of a frequency spectrum (e.g., an RF energylevel of all energy within the channel irrespective of its source).Measurement of signal strength(s) can be employed to minimize collisionsthat can occur between transmissions of groups of wireless devices. Forexample, when the signal strength(s) detected by the RX circuitry 410 dis at or above threshold(s), the CA logic 410 b can, in the logicalsense, stop/gate the communication of the TX data from the transmitbuffer 410 a to the TX circuitry 410 c. When the signal strength(s)detected by the RX circuitry 410 d are below the threshold, the CA logic410 b can, in the logical sense, allow data in the transmit buffer 410 ato be communicated to the TX circuitry 410 c. In some examples, afterthe signal strength(s) fall below the threshold(s), the CA logic canwait a random amount of time (e.g., between 0 and 500 ms) beforeallowing the data in the transmit buffer 410 a to be communicated to theTX circuitry 410 c. The random delay can help mitigate interference thatcan otherwise occur between transmissions from other similarly gatedwireless devices.

The TX circuitry 410 c is configured to generate a radio frequency (RF)signal based on the TX data, and to output the RF signal via the RX/TXswitch 410 e to an antenna 415. For example, the TX circuitry 410 c canbe configured to modulate the TX data within the 5 GHz spectrum. In thisregard, the TX circuitry 410 c can include a quadrature amplitudemodulator (QAM) to convert binary TX data to baseband in-phase andout-of-phase analog signals. The TX circuitry 410 c can include a mixerto modulate the in-phase and out-of-phase baseband analog signals to afrequency range within the 5 GHz spectrum. The TX circuitry 410 c caninclude a power amplifier to amplify the analog signals. In someexamples, similar operations can occur to modulate the TX data within adifferent RF spectrum, such as the 2.4 GHz spectrum.

The RX circuitry 410 d is configured to receive radio frequency (RF)signals via the RX/TX switch 410 e and to output received data (RXdata). For example, the RX circuitry 410 d can include one or moreamplifiers for amplifying RF signals received in the 2.4 GHz, 5 GHz,and/or 6 GHz spectrums. The RX circuitry 410 d can include a mixerconfigured to down-convert the RF signals to baseband in-phase andout-of-phase signals. The RX circuitry 410 d can include a QAMdemodulator to convert the baseband in-phase and out-of-phase signals toa binary pattern (i.e., RX data).

An example of the RX circuitry 410 d can be configured to measure thesignal strength (e.g., RSSI value) of received RF signals. Withinexamples, the RX circuitry 410 d can be configured to communicate thesignal strength(s) to the CA logic 410 b and/or the processor 405.

The RX/TX switch 410 e is configured to selectively couple the antenna415 to either the TX circuitry 410 c or the RX circuitry 410 d. Inoperation, when the TX circuitry 410 c is ready to transmit data, theRX/TX switch 410 e can be configured to couple the antenna 415 to the TXcircuitry 410 c. After the data has been transmitted, the RX/TX switch410 e can be configured to couple the antenna 415 to the RX circuitry410 d.

The antenna 415 is configured to radiate and/or detect electromagneticwaves. The antenna 415 may have any of a variety of constructions. Forexample, the antenna 415 can be a multi-band antenna (e.g., a dual-bandantenna) configured to operate on several frequency spectra (e.g., twoor more of: the 2.4 GHz spectrum, the 5 GHz spectrum, and the 6 GHzspectrum), such as a dual-band inverted-F antenna (IFA). In otherexamples, the antenna 415 can be a single-band antenna configured tooperate on a single frequency spectrum (e.g., the 2.4 GHz spectrum, the5 GHz spectrum, or the 6 GHz spectrum).

As noted above, the processor 405 can correspond to or include thecapabilities of the processor 112 a described above. For example, theprocessor 405 can communicate TX data, which can include audio contentsamples 300, to the wireless interface 410. The processor 405 canreceive RX data from the wireless interface 410. Within examples, the RXdata can include data related to user interactions with a particular SPD212, such as user actuation of a volume or mute control of the SPD 212.The RX data can include data related to simple network time protocol(SNTP) polling, which can be utilized by the SPDs 212 to facilitateclock synchronization with the MPD 210. The RX data can include signalstrength (e.g., RSSI level) measurements performed by wirelessinterfaces 410 of the SPDs 212. The signal strength measurements canrepresent the energy levels measured by the SPDs 212 that are associatedwith the transmission from the MPD 210 to the SPDs 212.

In some examples, the processor 405 can receive the signal strength(s)associated with signals detected by the wireless interface 410. In thiscase, the processor 405 can set the threshold(s) for the CA logic 410 bbased on the signal strength(s).

As noted above, the processor 405 can be in communication with thememory 112 b. The memory 112 b can store instruction code that isexecutable by the processor 405 for causing the processor 405 toimplement or facilitate performing various operations.

It should be appreciated that the wireless interface 400 shown in FIG. 4is only a logical diagram to facilitate description of various aspectsof the disclosure. Accordingly, a wireless interface implemented usingthe techniques described herein may include different components (e.g.,additional components, fewer components, etc.) arranged in a differentfashion than are shown in FIG. 4. For example, a wireless interfaceinterface that implements the techniques described herein may implementone or more functions of the CA logic 410 b in program instructionsexecuted by a processor (e.g., processor 405). Additionally (oralternatively), one or more components may be coupled between theelements shown in FIG. 4. For example, a diplexer may be coupled betweenthe antenna 415 and the RX/TX switch 410 e.

FIG. 5 illustrate examples of operations that can be performed by theprocessor 405 and/or the wireless interface 410 of a device (e.g., aplayback device) and/or a module for integration into a device tomitigate the interference issues described above. In this regard, thememory 112 b can store program instructions that are executable by theprocessor 405 to cause the processor 405 to perform one or more of theoperations shown in FIG. 5.

At block 500, the processor 405 can initialize the threshold(s) for theCA logic 410 b. For example, the device can set the threshold(s) to adefault value that is low enough to ensure that transmissions by thewireless interface 410 will not interfere with communications from theSPDs 212. For example, the processor 405 can set the threshold(s) to adefault value. In other examples, the processor 405 can set thethreshold(s) to a last used valued stored in memory. For example, theprocessor 405 may have previously determined an appropriate value forthe threshold(s) (e.g., by executing one or more operations shown inFIG. 5) and stored that those values in memory (e.g., memory 112 b). Inthis example, the processor 405 may retrieve those value(s) from memoryto use for initialization.

At block 505, the processor 405 can communicate TX data to the transmitbuffer 410 a. For example, the processor 405 can communicate TX dataassociated with one or more audio content samples 300 to the transmitbuffer 410 a. The TX data can specify a specific time at which each SPD212 should play corresponding channel samples associated with the one ormore audio content samples 300.

At block 510, the RX/TX switch 410 e can be configured to couple theantenna 415 to the RX circuitry 410 d. The RX circuitry 410 d can thenmonitor the signal strength(s) associated with any received networktraffic and communicate the signal strength(s) associated with anyreceived network traffic to the CA logic 410 b and/or to the processor405.

At block 515, if the signal strength(s) received from the RX circuitry410 d are at or above the threshold(s), the operations may continue fromblock 510. That is, the RX circuitry 410 d can continue to monitor thesignal strength(s) (e.g., RSSI levels associated with any receivednetwork traffic).

If the signal strength(s) received from the RX circuitry 410 d are belowthe threshold(s), then at block 520, the RX/TX switch 410 e can beconfigured to couple the antenna 415 to the TX circuitry 410 c. The CAlogic 410 b can then close to allow TX data in the transmit buffer 410 ato be communicated to the TX circuitry 410 c at block 520. The TXcircuitry 410 c can subsequently communicate the TX data tocorresponding SPDs 212.

At block 525, after transmission of the data has ceased, the RX/TXswitch 410 e can be configured to couple the antenna 415 to the RXcircuitry 410 d. The RX circuitry 410 d can then monitor the signalstrength(s) associated with any received network traffic and communicatethe signal strength(s) associated with any received network traffic tothe CA logic 410 b and to the processor 405. Signal strength(s)associated with transmissions from the SPDs 212 can be communicated tothe processor 405. Within examples, transmissions from the SPDs 212 canoccur in response to user interactions with the SPDs 212, such as useractuation of a volume or mute control of the SPDs 212. Communicationscan occur in response to simple network time protocol (SNTP) polling,which can be utilized by the SPDs 212 to facilitate clocksynchronization with the MPD 210. Communications can occur in responseto transmission of channel samples to the SPDs 212. Communications canoccur for other reasons.

At block 530, if the minimum signal strength(s) associated withcommunications from the SPDs 212 is within a margin of the currentthreshold(s) (e.g., 10 to 20 dbm greater than the threshold(s)), thenthe operations can repeat from block 505.

If the minimum signal strength(s) associated with communications fromthe SPDs 212 is not within the margin of the current signal strength(s),then at block 535, the threshold(s) can be modified to be within themargin above. For example, if the threshold(s) are below the minimumsignal strength(s) by more than, for example, 20 dbm, the threshold(s)can be adjusted upward to be within 10 to 20 dbm below the minimumsignal strength(s). If the threshold(s) are above the minimum signalstrength(s) or within, for example, 10 dbm of the minimum signalstrength(s), the threshold(s) can be adjusted downward to be within, forexample, 10 to 20 dbm below the minimum signal strength(s). Afteradjustment of the threshold(s), the operations can repeat from block505.

It should be appreciated that the particular values for variousthreshold(s) described herein are for illustrative purposes only and maybe set to any of a variety of values based on the particularimplementation. For example, the threshold(s) can be specified to be 25dbm below the minimum signal strength(s), 20 dbm below the minimumsignal strength(s), 15 dbm below the minimum signal strength(s), 10 dbmbelow the minimum signal strength(s), 5 dbm below the minimum signalstrength(s), 2 dbm below the minimum signal strength(s), or 1 dbm belowthe minimum signal strength(s).

FIGS. 6A and 6B are example timing diagrams that illustrate adjustmentof an example threshold (e.g., an RSSI threshold) in the operationsabove. Referring to FIG. 6A, the bottom timing diagram represents thetransmission of data from the wireless interface 410 of the MPD 210 tothe SPDs 212. For the sake of simplicity, the timing diagram assumes ahome theater environment 200 having four SPDs 212. Each block in thebottom timing diagram represents the transmission of one channel sample(e.g., FL1 of channel sample 305 a) to a corresponding SPD 212. Channelsamples 305 associated with a particular audio content sample 300 aregrouped together in the timing diagram.

The middle timing diagram represents the state of the CA logic 410 b atany given time. A high value for TX_(EN) indicates the CA logic 410 b islogically closed and, therefore, that the wireless circuitry cantransmit data stored in the transmit buffer 410 a to the SPDs 212. A lowvalue for TX_(EN) indicates the CA logic 410 b is logically open and,therefore, the transmission of the data stored in the transmit buffer410 a to the SPDs 212 is gated.

The top timing diagram depicts transmission blocks associated withtransmissions that can be received by the wireless interface 410 overtime. The amplitude of a particular transmission block represents therelative energy level of the transmission block as measured by the MPD210. The key indicates whether a particular transmission block isassociated with a transmission from an SPD 212 or another wirelessdevice 220.

For the sake of simplicity, each transmission block from a particularSPD 212 is shown as being communicated in response to the transmissionof a channel sample from the MPD 210. For example, each transmissionblock from a particular SPD 212 can indicate acknowledgment of receiptof a channel sample transmission from the MPD 210. However, in someexamples, an SPD 212 may not necessarily acknowledge receipt of thechannel sample. In these cases, the transmission block from a particularSPD 212 can correspond to, for example, a response to a polling requestsinitiated by the MPD 210, an SNTP transmission to synchronize aninternal clock of the SPD 212, and/or a transmission communicated inresponse to a user actuation of a control of the SPD 212 such as a muteor volume actuation. A transmission block could be associated with otherinformation communicated from the SPD 212.

The dashed line 607 running through the transmission blocks representsthe relative value of the RSSI threshold used by the CA logic 410 b todetermine whether to allow transmission of TX data.

During a first interval 615 a, the RSSI threshold 607 is set to aninitial/default value. The CA logic 410 b is enabled (i.e., closed).Therefore, the wireless interface 410 of the MPD 210 can transmit achannel sample associated with a first audio content sample o acorresponding SPD 212 and receive a response from the SPD 212. However,a transmission block 603 a associated with a transmission from anotherwireless device 220 occurs immediately afterward, and the transmissionhas an RSSI value that is above the RSSI threshold 607. Thus,transmission, by the MPD 210, of the remaining channel samples to thecorresponding SPDs 212 is gated/delayed until the transmission from theother wireless device 220 ends. (See delay D1.) Afterward, the MPD 210resumes transmission of the remaining channel samples and receives atransmission from each SPD 212. After receiving the transmissions fromeach SPD 212, the MPD 210 can determine a new RSSI threshold 607 basedon the RSSI values associated with the transmissions. During thisinterval, the RSSI threshold 607 is below the minimum RSSI level 610 a.Therefore, the MPD 210 increases the RSSI threshold 607 by anincremental amount to a value that is still below the energy level ofthe transmission block 610 a associated with the lowest energy level.

During a second interval 615 b, the wireless interface 410 of the MPD210 transmits channel samples associated with a second audio contentsample to corresponding SPDs 212 and receives responses from the SPDs212. As before, a transmission block 603 b from another wireless device220 that has an RSSI value above the RSSI threshold 607 occurs betweentransmission blocks of the SPDs 212. Thus, the transmission of certainchannel samples to the corresponding SPDs 212 is gated/delayed until thetransmission from the other wireless device 220 ends. (See delay D2.).Afterward, the MPD 210 resumes transmission of the remaining channelsamples and receives a transmission from each SPD 212. After receivingthe transmissions from each SPD 212, the MPD 210 can determine a newRSSI threshold 607 based on the RSSI values associated with thetransmissions. During the second interval, the RSSI threshold 607 isstill below the minimum RSSI level 610 b. Therefore, the MPD 210increases the RSS threshold 607 by an incremental amount to a value thatis still below the energy level of the transmission block 610 bassociated with the lowest energy level.

During a third and fourth interval (615 c and 614 d), the wirelessinterface 410 of the MPD 210 transmits a channel sample associated withthird and fourth audio content samples to corresponding SPDs 212 andreceives responses from the SPDs 212. As before, transmission blocks(603 c and 603 d) associated with another wireless device 220 occur.However, in these cases, the RSSI level of the transmission blocks (603c and 603 d) from the other wireless device 220 is below the currentRSSI threshold 607. Therefore, no additional delay is incurred betweentransmissions of the channel samples to the corresponding SPDs 212. TheMPD 210 can maintain the value of the RSSI threshold.

Referring to FIG. 6B, during a fifth interval 615 e, the wirelessinterface 410 of the MPD 210 transmits a channel sample associated witha fifth audio content sample to corresponding SPDs 212 and receivesresponses from the SPDs 212. As before, transmissions from anotherwireless device 220 occur during this interval. However, no additionaldelay is incurred between the transmission of the channel samplesbecause the RSSI level of transmissions from the other wireless device220 is below the RSSI threshold 607. However, the RSSI level 620 aassociated with a particular transmission from a particular SPD 212 isbelow the RSSI threshold 607. Therefore, the MPD 210 can lower the RSSIthreshold 607 to be below the RSSI level associated with thetransmission from the SPD 212.

In the timing diagrams above, the RSSI threshold 607 incrementally movesto be within a margin of the RSSI value associated with the SPD 212having the lowest associated RSSI level. For example, the RSSI threshold607 can be adjusted by a fixed amount during each iteration. In someexamples, the RSSI threshold 607 can be set in one iteration to bewithin the margin. Still, in other examples, the amount by which theRSSI threshold 607 is adjusted can be different during differentintervals. For example, the RSSI threshold 607 can be adjusted accordingto an algorithm such as a steepest descent algorithm to facilitatecoming to within a margin of the lowest RSSI value more quickly.

Still, in other examples, the RSSI threshold 607 can be adjusted aftermultiple audio content samples have been communicated to the SPDs. Forexample, after the channel samples for a group of audio content sampleshave been communicated to the SPDs, and responses have been receivedfrom the SPDs, the average (e.g., moving average) minimum RSSI level canbe used as the basis for adjusting the RSSI threshold 607. This processcan repeat after a particular number of audio content samples (e.g., 100samples) have been communicated and/or after a certain amount of timehas passed (e.g., 2 seconds).

In some examples, one or more components of the logical diagram 400 ofFIG. 4 can be implemented by a dedicated transceiver. An example of sucha receiver can be an 802.11 (e.g., 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.11ax, etc.) transceiver. The 802.11 transceiver caninclude registers that facilitate setting the above-referencedthreshold(s) and circuitry for performing the operations of the CAlogic. For example, the 802.11 transceiver can include one or moreregisters that facilitate setting a signal detect (SD) threshold and/oran energy detect (ED) threshold of clear channel assessment logic (CCAlogic). The value of the SD threshold register and/or the ED thresholdregister can be set to correspond to the above referenced threshold(s).The SD threshold register and/or the ED threshold register can bedynamically adjusted, as indicated above, to be within a margin of thelowest signal strength(s) (e.g., RSSI levels) associated with the SPDs212.

Further, while the logical diagram 400 of FIG. 4 is described as beingpart of an MBP 210, which can include one or more speakers, a powersupply, housing, etc. in some examples, one or more of more componentsof the circuitry can be provided on a module. An example of the modulecan include a circuit board. A wireless network interface, audio inputinterface, one or more processors, and data storage can be mounted onthe circuit board. Within examples, the wireless network interface andthe one or more processors can implement the operations of the processor405 and the wireless interface 410 of FIG. 4. The data storage can storeinstructions that, when executed by the one or more processors, causethe module to perform one or more of the operations described above.

FIG. 7 illustrates an example of a wireless transceiver 705 that canperform the latency reduction techniques described herein. Referring toFIG. 7, the wireless transceiver 705 can include a processor 710 and amemory 715, such as read-only memory (ROM) for storing instruction code(e.g., firmware) for execution by the processor 710. The processor 710can be separate and distinct from the processor 405 of FIG. 4. Firmwarecan be stored in the memory 715 and can be executed by the processor 710to cause the processor 710 to perform the functionality implemented bythe processor 405 of FIG. 4 with respect to the modification of thethreshold(s). In this example, the processor 405 of FIG. 4 can be usedinstead to handle aspects related to receiving audio from an audiosource and communicating audio content samples to the wirelesstransceiver 705. In some examples, driver instruction code can beexecuted by the first processor 405 to cause the first processor todownload firmware instructions into the memory 715 of the wirelesstransceiver 705 for causing the processor 710 of the wirelesstransceiver 705 to perform the threshold modification functionalitydescribed above.

It should be appreciated that the wireless interface 700 shown in FIG. 7is only a logical diagram to facilitate description of various aspectsof the disclosure. Accordingly, a wireless transceiver implemented usingthe techniques described herein may include different components (e.g.,additional components, fewer components, etc.) arranged in a differentfashion than are shown in FIG. 7. For example, a wireless transceiverthat implements the techniques described herein may not include theRX/TX switch 310 e.

FIG. 8 illustrates a variation of the operations performed above. Block800 can involve determining, by the first playback device, a first RFenergy level associated with RF signal communications from a secondplayback device to the first playback device.

Block 805 can involve modifying, by the first playback device, athreshold RF energy level for holding off transmissions by the firstplayback device to be within a threshold amount of the first RF energylevel.

Block 810 can involve receiving, by the first playback device,multi-channel audio content via an audio input interface.

Block 815 can involve detecting an ambient RF energy level.

Block 820 can involve, based on the ambient RF energy level being belowthe threshold RF energy level, wirelessly communicating data thatrepresents a channel of the multi-channel audio content to the secondplayback device for playback by the second playback device in synchronywith playback of one or more other channels of the multi-channel audiocontent by the first playback device.

Some examples can involve determining, by the first playback device, asecond RF energy level associated with second RF signal communicationsfrom a third playback device to the first playback device; andspecifying the threshold RF energy level for holding off thetransmissions by the first playback device to be within a thresholdamount of a lower of the first RF energy level and the second RF energylevel.

In some examples, determining the first RF energy level associated withRF signal communications can involve determining the first RF energylevel based on a received signal strength indicator message (RSSImessage) communicated from the second playback device to the firstplayback device.

In some examples, the ambient RF energy level corresponds to an RFenergy level associated with an RF channel through which the firstplayback device communicates with the second playback device.

In some examples, the first playback device comprises an 802.11 basedtransceiver. These examples can involve setting, by the first playbackdevice, a signal detect (SD) threshold and/or an energy detect (ED)threshold of clear channel assessment (CCA) logic of the 802.11 basedtransceiver to value(s) associated with the threshold RF energy level.

IV. Conclusion

The above discussions relating to playback devices, controller devices,playback zone configurations, and media content sources provide onlysome examples of operating environments within which functions andmethods described below may be implemented. Other operating environmentsand configurations of media playback systems, playback devices, andnetwork devices not explicitly described herein may also be applicableand suitable for the implementation of the functions and methods.

The description above discloses, among other things, various examplesystems, methods, apparatus, and articles of manufacture including,among other components, firmware and/or software executed on hardware.It is understood that such examples are merely illustrative and shouldnot be considered as limiting. For example, it is contemplated that anyor all of the firmware, hardware, and/or software aspects or componentscan be embodied exclusively in hardware, exclusively in software,exclusively in firmware, or in any combination of hardware, software,and/or firmware. Accordingly, the examples provided are not the onlyways to implement such systems, methods, apparatus, and/or articles ofmanufacture.

It should be appreciated that the latency reduction techniques may beadvantageously implemented in any of a variety devices (e.g., playbackdevices) separate and apart from those specific playback devicesconfigured to receive audio content from a television. For example, thelatency reduction techniques may be readily integrated into a televisionitself (or any other playback device that displays video content) thatwirelessly communicates the audio content to other devices (e.g., asoundbar, a sub, rear satellites, etc.) for playback in synchrony withthe displayed video content. While such a television could simply delayoutput of the video content to accommodate the time needed tosuccessfully transmit all the audio to the other devices for playback,such a design would undesirably increase the input lag of thetelevision. Thus, the latency reduction techniques described herein maybe readily implemented in such a television (or any other playbackdevice that displays video content) so as to limit (and/or eliminate)the delay that would need to otherwise be introduced to accommodate thewireless transmission of the audio content to the requisite devices.

Additionally, references herein to “embodiment” means that a particularfeature, structure, or characteristic described in connection with theembodiment can be included in at least one example embodiment of aninvention. The appearances of this phrase in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments mutually exclusive of otherembodiments. As such, the embodiments described herein, explicitly andimplicitly understood by one skilled in the art, can be combined withother embodiments.

The specification is presented largely in terms of illustrativeenvironments, systems, procedures, steps, logic blocks, processing, andother symbolic representations that directly or indirectly resemble theoperations of data processing devices coupled to networks. These processdescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art. Numerous specific details are set forth to provide athorough understanding of the present disclosure. However, it isunderstood to those skilled in the art that certain embodiments of thepresent disclosure can be practiced without certain, specific details.In other instances, well-known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the embodiments. Accordingly, the scope of thepresent disclosure is defined by the appended claims rather than theforegoing description of embodiments.

When any of the appended claims are read to cover a purely softwareand/or firmware implementation, at least one of the elements in at leastone example is hereby expressly defined to include a tangible,non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on,storing the software and/or firmware.

V. Example Features

(Feature 1) A first playback device comprising: a wireless networkinterface; an audio input interface; one or more processors; at leastone non-transitory computer-readable medium; and program instructionsstored on the non-transitory computer-readable medium that areexecutable by the at least one processor such that the first playbackdevice is configured to: determine a first radio frequency (RF) energylevel associated with RF signal communications from a second playbackdevice to the first playback device; modify a threshold RF energy levelfor holding off transmissions by the first playback device based on thefirst RF energy level; and after receipt of multi-channel audio contentvia the audio input interface, detect an ambient RF energy level; andbased on the ambient RF energy level and the threshold RF energy level,communicate, via the wireless network interface, data that represents achannel of the multi-channel audio content to the second playback devicefor playback by the second playback device in synchrony with playback ofone or more other channels of the multi-channel audio content by thefirst playback device.

(Feature 2) The first playback device of feature 1, further comprisingprogram instructions stored on the at least one non-transitorycomputer-readable medium that are executable by the at least oneprocessor such that the first playback device is configured to:determine a second RF energy level associated with second RF signalcommunications from a third playback device to the first playbackdevice; and increase the threshold RF energy level for holding off thetransmissions by the first playback device to be within a thresholdamount of a lower of the first RF energy level and the second RF energylevel.

(Feature 3) The first playback device of feature 1 or 2, furthercomprising program instructions stored on the at least onenon-transitory computer-readable medium that are executable by the atleast one processor such that the first playback device is configuredto: determine the first RF energy level based on one or more receivedsignal strength indicator (RSSI) values associated with at least onemessage communicated from the second playback device to the firstplayback device.

(Feature 4) The first playback device of any of features 1-3, furthercomprising program instructions stored on the at least onenon-transitory computer-readable medium that are executable by the atleast one processor such that the first playback device is configuredto: determine that the RF signal communications from the second playbackdevice have ceased; and incrementally lower the threshold RF energylevel until the RF signal communications from the second playback deviceresume.

(Feature 5) The first playback device of feature 4, wherein the programinstructions that are executable by the at least one processor such thatthe first playback device is configured to determine that the RF signalcommunications from the second playback device have ceased comprisesprogram instructions that are executable by the at least one processorsuch that the first playback device is configured to: receive anindication from the second playback device, via a third playback devicein communication with both the first playback device and the secondplayback device, that the RF signal communications have ceased.

(Feature 6) The first playback device of any of features 1-5, whereinthe ambient RF energy level corresponds to an RF energy level associatedwith an RF channel through which the first playback device communicateswith the second playback device.

(Feature 7) The first playback device of any of features 1-6, whereinthe multi-channel audio content is synchronized to video content,wherein an audio delay between the multi-channel audio content receivedvia the audio input interface and the multi-channel audio content playedfrom the second playback device is less than 40 ms.

(Feature 8) The first playback device of any of features 1-7, whereinthe first playback device communicates the multi-channel audio contentto the second playback device over a 20 Mhz channel in a 5 GHz frequencyspectrum.

(Feature 9) The first playback device of any of features 1-8, whereinthe wireless network interface comprises an 802.11 based transceiver andwherein the threshold RF energy level for holding off wirelesstransmissions comprises at least one of: a signal detect (SD) thresholdof a clear channel assessment logic in the 802.11 based transceiver oran energy detect (ED) threshold of the clear channel assessment logic inthe 802.11 based transceiver.

(Feature 10) The first playback device of any of features 1-9, whereinthe threshold RF energy is specified to be 10 dbm below the first RFenergy level, 5 dbm below the first RF energy level, or 2 dbm below thefirst RF energy level.

(Feature 11) The first playback device of any of features 1-10, whereinthe one or more processors include a first processor integrated into awireless transceiver and a second processor that is separate anddistinct from the wireless transceiver, and wherein the at least onenon-transitory computer-readable medium comprises a read-only memory(ROM) storing a first portion of the program instructions executed bythe first processor and a read-write memory storing a second portion ofthe program instructions executed by the second processor.

(Feature 12) A method performed by a first playback device of a hometheater system comprising: determining, by the first playback device, afirst radio frequency (RF) energy level associated with RF signalcommunications from a second playback device to the first playbackdevice; modifying, by the first playback device, a threshold RF energylevel for holding off transmissions by the first playback device to bewithin a threshold amount of the first RF energy level; receiving, bythe first playback device, multi-channel audio content via an audioinput interface; detecting an ambient RF energy level; and based on theambient RF energy level being below the threshold RF energy level,wirelessly communicating data that represents a channel of themulti-channel audio content to the second playback device for playbackby the second playback device in synchrony with playback of one or moreother channels of the multi-channel audio content by the first playbackdevice.

(Feature 13) The method of feature 12, further comprising: determining,by the first playback device, a second RF energy level associated withsecond RF signal communications from a third playback device to thefirst playback device; and specifying the threshold RF energy level forholding off the transmissions by the first playback device to be withina threshold amount of a lower of the first RF energy level and thesecond RF energy level.

(Feature 14) The method of feature 12 or 13, wherein determining thefirst RF energy level associated with RF signal communications furthercomprises determining the first RF energy level based on a receivedsignal strength indicator message (RSSI message) communicated from thesecond playback device to the first playback device.

(Feature 15) The method of any of features 12-14, wherein the ambient RFenergy level corresponds to an RF energy level associated with an RFchannel through which the first playback device communicates with thesecond playback device.

(Feature 16) The method of any of features 12-15, wherein the firstplayback device comprises an 802.11 based transceiver, wherein themethod comprises setting, by the first playback device, a signal detectthreshold (SD threshold) of clear channel assessment logic (CCA logic)of the 802.11 based transceiver to a value associated with the thresholdRF energy level.

(Feature 17) Circuitry for a playback device, the circuitry comprising:a wireless network interface; an audio input interface; one or moreprocessors; at least one non-transitory computer-readable medium; andprogram instructions stored on the non-transitory computer-readablemedium that are executable by the at least one processor such that aplayback device into which the circuitry is integrated is configured to:determine a first radio frequency (RF) energy level associated with RFsignal communications from another playback device; modify a thresholdRF energy level for holding off wireless transmissions via the wirelessnetwork interface based on the first RF energy level; and after receiptof multi-channel audio content via the audio input interface, detect anambient RF energy level; and based on the ambient RF energy level andthe threshold RF energy level, communicate, via the wireless networkinterface, data that represents a channel of the multi-channel audiocontent to the other playback device for playback by the other playbackdevice in synchrony with playback of one or more other channels of themulti-channel audio content by a playback device into which thecircuitry is integrated.

(Feature 18) The circuitry of feature 17, further comprising at leastone circuit board and wherein at least one of: the wireless networkinterface, the audio input interface, the one or more processors, or theat least one non-transitory computer-readable medium is attached to theat least one circuit board.

(Feature 19) The circuitry of feature 17 or 18, further comprisingprogram instructions stored on the at least one non-transitorycomputer-readable medium that are executable by the at least oneprocessor such that a playback device into which the circuitry isintegrated is configured to: determine the first RF energy level basedon a received signal strength indicator message (RSSI message)communicated from the other playback device.

(Feature 20) The circuitry of any of features 17-19, wherein the ambientRF energy level corresponds to an RF energy level associated with an RFchannel through which the circuitry communicates with the secondplayback device.

(Feature 21) The circuitry of any of features 17-20, wherein thewireless network interface comprises an 802.11 based transceiver andwherein the threshold RF energy level for holding off wirelesstransmissions comprises at least one of: a signal detect (SD) thresholdof a clear channel assessment logic in the 802.11 based transceiver oran energy detect (ED) threshold of the clear channel assessment logic inthe 802.11 based transceiver.

(Feature 22) A first playback device comprising: a wireless networkinterface; a media input interface; one or more processors; at least onenon-transitory computer-readable medium; and program instructions storedon the non-transitory computer-readable medium that are executable bythe at least one processor such that the first playback device isconfigured to: determine a first radio frequency (RF) energy levelassociated with RF signal communications from a second playback deviceto the first playback device; modify a sensitivity of a collisionavoidance mechanism for holding off transmissions by the first playbackdevice based on the first RF energy level; and after receipt of mediacontent via the media input interface, detect an ambient RF energylevel; and based on the ambient RF energy level and the threshold RFenergy level, communicate, via the wireless network interface, data thatrepresents a first portion of the media content to the second playbackdevice for playback by the second playback device in synchrony withplayback of a second portion of the media content by the first playbackdevice.

(Feature 23) The first playback device of feature 22, wherein the firstplayback device is a television, the first portion of the media contentcomprises audio content, and the second portion of the media contentcomprises video content.

(Feature 24) The first playback device of feature 22 or 23, wherein thesecond playback device is a soundbar.

The invention claimed is:
 1. A first playback device comprising: a wireless network interface; an audio input interface; one or more processors; at least one non-transitory computer-readable medium; and program instructions stored on the non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to: determine a first radio frequency (RF) energy level associated with RF signal communications from a second playback device to the first playback device; modify a threshold RF energy level for holding off transmissions by the first playback device based on the first RF energy level; and after receipt of multi-channel audio content via the audio input interface, detect an ambient RF energy level of wireless activity in at least one wireless channel; and based on the ambient RF energy level and the threshold RF energy level, communicate, via the wireless network interface, data that represents a channel of the multi-channel audio content to the second playback device for playback by the second playback device in synchrony with playback of one or more other channels of the multi-channel audio content by the first playback device.
 2. The first playback device of claim 1, further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to: determine a second RF energy level associated with second RF signal communications from a third playback device to the first playback device; and increase the threshold RF energy level for holding off the transmissions by the first playback device to be within a threshold amount of a lower of the first RF energy level and the second RF energy level.
 3. The first playback device of claim 1, further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to: determine the first RF energy level based on one or more received signal strength indicator (RSSI) values associated with at least one message communicated from the second playback device to the first playback device.
 4. The first playback device of claim 1, further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to: determine that the RF signal communications from the second playback device have ceased; and incrementally lower the threshold RF energy level until the RF signal communications from the second playback device resume.
 5. The first playback device of claim 4, wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to determine that the RF signal communications from the second playback device have ceased comprises program instructions that are executable by the at least one processor such that the first playback device is configured to: receive an indication from the second playback device, via a third playback device in communication with both the first playback device and the second playback device, that the RF signal communications have ceased.
 6. The first playback device of claim 1, wherein the ambient RF energy level corresponds to an RF energy level associated with an RF channel through which the first playback device communicates with the second playback device.
 7. The first playback device of claim 1, wherein the multi-channel audio content is synchronized to video content, wherein an audio delay between the multi-channel audio content received via the audio input interface and the multi-channel audio content played from the second playback device is less than 40 ms.
 8. The first playback device of claim 1, wherein the first playback device communicates the multi-channel audio content to the second playback device over a 20 Mhz channel in a 5 GHz frequency spectrum.
 9. The first playback device of claim 1, wherein the wireless network interface comprises an 802.11 based transceiver and wherein the threshold RF energy level for holding off wireless transmissions comprises at least one of: a signal detect (SD) threshold of a clear channel assessment logic in the 802.11 based transceiver or an energy detect (ED) threshold of the clear channel assessment logic in the 802.11 based transceiver.
 10. The first playback device of claim 1, wherein the threshold RF energy is specified to be 10 dbm below the first RF energy level, 5 dbm below the first RF energy level, or 2 dbm below the first RF energy level.
 11. The first playback device of claim 1, wherein the one or more processors include a first processor integrated into a wireless transceiver and a second processor that is separate and distinct from the wireless transceiver, and wherein the at least one non-transitory computer-readable medium comprises a read-only memory (ROM) storing a first portion of the program instructions executed by the first processor and a read-write memory storing a second portion of the program instructions executed by the second processor.
 12. A method performed by a first playback device of a home theater system comprising: determining, by the first playback device, a first radio frequency (RF) energy level associated with RF signal communications from a second playback device to the first playback device; modifying, by the first playback device, a threshold RF energy level for holding off transmissions by the first playback device to be within a threshold amount of the first RF energy level; receiving, by the first playback device, multi-channel audio content via an audio input interface; detecting an ambient RF energy level of wireless activity in at least one wireless channel; and based on the ambient RF energy level being below the threshold RF energy level, wirelessly communicating data that represents a channel of the multi-channel audio content to the second playback device for playback by the second playback device in synchrony with playback of one or more other channels of the multi-channel audio content by the first playback device.
 13. The method of claim 12, further comprising: determining, by the first playback device, a second RF energy level associated with second RF signal communications from a third playback device to the first playback device; and specifying the threshold RF energy level for holding off the transmissions by the first playback device to be within a threshold amount of a lower of the first RF energy level and the second RF energy level.
 14. The method of claim 12, wherein determining the first RF energy level associated with RF signal communications further comprises determining the first RF energy level based on a received signal strength indicator message (RSSI message) communicated from the second playback device to the first playback device.
 15. The method of claim 12, wherein the ambient RF energy level corresponds to an RF energy level associated with an RF channel through which the first playback device communicates with the second playback device.
 16. The method of claim 12, wherein the first playback device comprises an 802.11 based transceiver, wherein the method comprises setting, by the first playback device, a signal detect threshold (SD threshold) of clear channel assessment logic (CCA logic) of the 802.11 based transceiver to a value associated with the threshold RF energy level.
 17. Circuitry for a playback device, the circuitry comprising: a wireless network interface; an audio input interface; one or more processors; at least one non-transitory computer-readable medium; and program instructions stored on the non-transitory computer-readable medium that are executable by the at least one processor such that a playback device into which the circuitry is integrated is configured to: determine a first radio frequency (RF) energy level associated with RF signal communications from another playback device; modify a threshold RF energy level for holding off wireless transmissions via the wireless network interface based on the first RF energy level; and after receipt of multi-channel audio content via the audio input interface, detect an ambient RF energy level of wireless activity in at least one wireless channel; and based on the ambient RF energy level and the threshold RF energy level, communicate, via the wireless network interface, data that represents a channel of the multi-channel audio content to the other playback device for playback by the other playback device in synchrony with playback of one or more other channels of the multi-channel audio content by a playback device into which the circuitry is integrated.
 18. The circuitry of claim 17, further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that a playback device into which the circuitry is integrated is configured to: determine the first RF energy level based on a received signal strength indicator message (RSSI message) communicated from the other playback device.
 19. The circuitry of claim 17, wherein the ambient RF energy level corresponds to an RF energy level associated with an RF channel through which the circuitry communicates with the second playback device.
 20. The circuitry of claim 17, wherein the wireless network interface comprises an 802.11 based transceiver and wherein the threshold RF energy level for holding off wireless transmissions comprises at least one of: a signal detect (SD) threshold of a clear channel assessment logic in the 802.11 based transceiver or an energy detect (ED) threshold of the clear channel assessment logic in the 802.11 based transceiver. 